"""Laplace Transforms""" import sys import sympy from sympy.core import S, pi, I from sympy.core.add import Add from sympy.core.cache import cacheit from sympy.core.expr import Expr from sympy.core.function import ( AppliedUndef, Derivative, expand, expand_complex, expand_mul, expand_trig, Lambda, WildFunction, diff, Subs) from sympy.core.mul import Mul, prod from sympy.core.relational import ( _canonical, Ge, Gt, Lt, Unequality, Eq, Ne, Relational) from sympy.core.sorting import ordered from sympy.core.symbol import Dummy, symbols, Wild from sympy.functions.elementary.complexes import ( re, im, arg, Abs, polar_lift, periodic_argument) from sympy.functions.elementary.exponential import exp, log from sympy.functions.elementary.hyperbolic import cosh, coth, sinh, asinh from sympy.functions.elementary.miscellaneous import Max, Min, sqrt from sympy.functions.elementary.piecewise import ( Piecewise, piecewise_exclusive) from sympy.functions.elementary.trigonometric import cos, sin, atan, sinc from sympy.functions.special.bessel import besseli, besselj, besselk, bessely from sympy.functions.special.delta_functions import DiracDelta, Heaviside from sympy.functions.special.error_functions import erf, erfc, Ei from sympy.functions.special.gamma_functions import ( digamma, gamma, lowergamma, uppergamma) from sympy.functions.special.singularity_functions import SingularityFunction from sympy.integrals import integrate, Integral from sympy.integrals.transforms import ( _simplify, IntegralTransform, IntegralTransformError) from sympy.logic.boolalg import to_cnf, conjuncts, disjuncts, Or, And from sympy.matrices.matrixbase import MatrixBase from sympy.polys.matrices.linsolve import _lin_eq2dict from sympy.polys.polyerrors import PolynomialError from sympy.polys.polyroots import roots from sympy.polys.polytools import Poly from sympy.polys.rationaltools import together from sympy.polys.rootoftools import RootSum from sympy.utilities.exceptions import ( sympy_deprecation_warning, SymPyDeprecationWarning, ignore_warnings) from sympy.utilities.misc import debugf _LT_level = 0 def DEBUG_WRAP(func): def wrap(*args, **kwargs): from sympy import SYMPY_DEBUG global _LT_level if not SYMPY_DEBUG: return func(*args, **kwargs) if _LT_level == 0: print('\n' + '-'*78, file=sys.stderr) print('-LT- %s%s%s' % (' '*_LT_level, func.__name__, args), file=sys.stderr) _LT_level += 1 if ( func.__name__ == '_laplace_transform_integration' or func.__name__ == '_inverse_laplace_transform_integration'): sympy.SYMPY_DEBUG = False print('**** %sIntegrating ...' % (' '*_LT_level), file=sys.stderr) result = func(*args, **kwargs) sympy.SYMPY_DEBUG = True else: result = func(*args, **kwargs) _LT_level -= 1 print('-LT- %s---> %s' % (' '*_LT_level, result), file=sys.stderr) if _LT_level == 0: print('-'*78 + '\n', file=sys.stderr) return result return wrap def _debug(text): from sympy import SYMPY_DEBUG global _LT_level if SYMPY_DEBUG: print('-LT- %s%s' % (' '*_LT_level, text), file=sys.stderr) def _simplifyconds(expr, s, a): r""" Naively simplify some conditions occurring in ``expr``, given that `\operatorname{Re}(s) > a`. Examples ======== >>> from sympy.integrals.laplace import _simplifyconds >>> from sympy.abc import x >>> from sympy import sympify as S >>> _simplifyconds(abs(x**2) < 1, x, 1) False >>> _simplifyconds(abs(x**2) < 1, x, 2) False >>> _simplifyconds(abs(x**2) < 1, x, 0) Abs(x**2) < 1 >>> _simplifyconds(abs(1/x**2) < 1, x, 1) True >>> _simplifyconds(S(1) < abs(x), x, 1) True >>> _simplifyconds(S(1) < abs(1/x), x, 1) False >>> from sympy import Ne >>> _simplifyconds(Ne(1, x**3), x, 1) True >>> _simplifyconds(Ne(1, x**3), x, 2) True >>> _simplifyconds(Ne(1, x**3), x, 0) Ne(1, x**3) """ def power(ex): if ex == s: return 1 if ex.is_Pow and ex.base == s: return ex.exp return None def bigger(ex1, ex2): """ Return True only if |ex1| > |ex2|, False only if |ex1| < |ex2|. Else return None. """ if ex1.has(s) and ex2.has(s): return None if isinstance(ex1, Abs): ex1 = ex1.args[0] if isinstance(ex2, Abs): ex2 = ex2.args[0] if ex1.has(s): return bigger(1/ex2, 1/ex1) n = power(ex2) if n is None: return None try: if n > 0 and (Abs(ex1) <= Abs(a)**n) == S.true: return False if n < 0 and (Abs(ex1) >= Abs(a)**n) == S.true: return True except TypeError: return None def replie(x, y): """ simplify x < y """ if (not (x.is_positive or isinstance(x, Abs)) or not (y.is_positive or isinstance(y, Abs))): return (x < y) r = bigger(x, y) if r is not None: return not r return (x < y) def replue(x, y): b = bigger(x, y) if b in (True, False): return True return Unequality(x, y) def repl(ex, *args): if ex in (True, False): return bool(ex) return ex.replace(*args) from sympy.simplify.radsimp import collect_abs expr = collect_abs(expr) expr = repl(expr, Lt, replie) expr = repl(expr, Gt, lambda x, y: replie(y, x)) expr = repl(expr, Unequality, replue) return S(expr) @DEBUG_WRAP def expand_dirac_delta(expr): """ Expand an expression involving DiractDelta to get it as a linear combination of DiracDelta functions. """ return _lin_eq2dict(expr, expr.atoms(DiracDelta)) @DEBUG_WRAP def _laplace_transform_integration(f, t, s_, *, simplify): """ The backend function for doing Laplace transforms by integration. This backend assumes that the frontend has already split sums such that `f` is to an addition anymore. """ s = Dummy('s') if f.has(DiracDelta): return None F = integrate(f*exp(-s*t), (t, S.Zero, S.Infinity)) if not F.has(Integral): return _simplify(F.subs(s, s_), simplify), S.NegativeInfinity, S.true if not F.is_Piecewise: return None F, cond = F.args[0] if F.has(Integral): return None def process_conds(conds): """ Turn ``conds`` into a strip and auxiliary conditions. """ from sympy.solvers.inequalities import _solve_inequality a = S.NegativeInfinity aux = S.true conds = conjuncts(to_cnf(conds)) p, q, w1, w2, w3, w4, w5 = symbols( 'p q w1 w2 w3 w4 w5', cls=Wild, exclude=[s]) patterns = ( p*Abs(arg((s + w3)*q)) < w2, p*Abs(arg((s + w3)*q)) <= w2, Abs(periodic_argument((s + w3)**p*q, w1)) < w2, Abs(periodic_argument((s + w3)**p*q, w1)) <= w2, Abs(periodic_argument((polar_lift(s + w3))**p*q, w1)) < w2, Abs(periodic_argument((polar_lift(s + w3))**p*q, w1)) <= w2) for c in conds: a_ = S.Infinity aux_ = [] for d in disjuncts(c): if d.is_Relational and s in d.rhs.free_symbols: d = d.reversed if d.is_Relational and isinstance(d, (Ge, Gt)): d = d.reversedsign for pat in patterns: m = d.match(pat) if m: break if m and m[q].is_positive and m[w2]/m[p] == pi/2: d = -re(s + m[w3]) < 0 m = d.match(p - cos(w1*Abs(arg(s*w5))*w2)*Abs(s**w3)**w4 < 0) if not m: m = d.match( cos(p - Abs(periodic_argument(s**w1*w5, q))*w2) * Abs(s**w3)**w4 < 0) if not m: m = d.match( p - cos( Abs(periodic_argument(polar_lift(s)**w1*w5, q))*w2 )*Abs(s**w3)**w4 < 0) if m and all(m[wild].is_positive for wild in [ w1, w2, w3, w4, w5]): d = re(s) > m[p] d_ = d.replace( re, lambda x: x.expand().as_real_imag()[0]).subs(re(s), t) if ( not d.is_Relational or d.rel_op in ('==', '!=') or d_.has(s) or not d_.has(t)): aux_ += [d] continue soln = _solve_inequality(d_, t) if not soln.is_Relational or soln.rel_op in ('==', '!='): aux_ += [d] continue if soln.lts == t: return None else: a_ = Min(soln.lts, a_) if a_ is not S.Infinity: a = Max(a_, a) else: aux = And(aux, Or(*aux_)) return a, aux.canonical if aux.is_Relational else aux conds = [process_conds(c) for c in disjuncts(cond)] conds2 = [x for x in conds if x[1] != S.false and x[0] is not S.NegativeInfinity] if not conds2: conds2 = [x for x in conds if x[1] != S.false] conds = list(ordered(conds2)) def cnt(expr): if expr in (True, False): return 0 return expr.count_ops() conds.sort(key=lambda x: (-x[0], cnt(x[1]))) if not conds: return None a, aux = conds[0] # XXX is [0] always the right one? def sbs(expr): return expr.subs(s, s_) if simplify: F = _simplifyconds(F, s, a) aux = _simplifyconds(aux, s, a) return _simplify(F.subs(s, s_), simplify), sbs(a), _canonical(sbs(aux)) @DEBUG_WRAP def _laplace_deep_collect(f, t): """ This is an internal helper function that traverses through the epression tree of `f(t)` and collects arguments. The purpose of it is that anything like `f(w*t-1*t-c)` will be written as `f((w-1)*t-c)` such that it can match `f(a*t+b)`. """ if not isinstance(f, Expr): return f if (p := f.as_poly(t)) is not None: return p.as_expr() func = f.func args = [_laplace_deep_collect(arg, t) for arg in f.args] return func(*args) @cacheit def _laplace_build_rules(): """ This is an internal helper function that returns the table of Laplace transform rules in terms of the time variable `t` and the frequency variable `s`. It is used by ``_laplace_apply_rules``. Each entry is a tuple containing: (time domain pattern, frequency-domain replacement, condition for the rule to be applied, convergence plane, preparation function) The preparation function is a function with one argument that is applied to the expression before matching. For most rules it should be ``_laplace_deep_collect``. """ t = Dummy('t') s = Dummy('s') a = Wild('a', exclude=[t]) b = Wild('b', exclude=[t]) n = Wild('n', exclude=[t]) tau = Wild('tau', exclude=[t]) omega = Wild('omega', exclude=[t]) def dco(f): return _laplace_deep_collect(f, t) _debug('_laplace_build_rules is building rules') laplace_transform_rules = [ (a, a/s, S.true, S.Zero, dco), # 4.2.1 (DiracDelta(a*t-b), exp(-s*b/a)/Abs(a), Or(And(a > 0, b >= 0), And(a < 0, b <= 0)), S.NegativeInfinity, dco), # Not in Bateman54 (DiracDelta(a*t-b), S(0), Or(And(a < 0, b >= 0), And(a > 0, b <= 0)), S.NegativeInfinity, dco), # Not in Bateman54 (Heaviside(a*t-b), exp(-s*b/a)/s, And(a > 0, b > 0), S.Zero, dco), # 4.4.1 (Heaviside(a*t-b), (1-exp(-s*b/a))/s, And(a < 0, b < 0), S.Zero, dco), # 4.4.1 (Heaviside(a*t-b), 1/s, And(a > 0, b <= 0), S.Zero, dco), # 4.4.1 (Heaviside(a*t-b), 0, And(a < 0, b > 0), S.Zero, dco), # 4.4.1 (t, 1/s**2, S.true, S.Zero, dco), # 4.2.3 (1/(a*t+b), -exp(-b/a*s)*Ei(-b/a*s)/a, Abs(arg(b/a)) < pi, S.Zero, dco), # 4.2.6 (1/sqrt(a*t+b), sqrt(a*pi/s)*exp(b/a*s)*erfc(sqrt(b/a*s))/a, Abs(arg(b/a)) < pi, S.Zero, dco), # 4.2.18 ((a*t+b)**(-S(3)/2), 2*b**(-S(1)/2)-2*(pi*s/a)**(S(1)/2)*exp(b/a*s) * erfc(sqrt(b/a*s))/a, Abs(arg(b/a)) < pi, S.Zero, dco), # 4.2.20 (sqrt(t)/(t+b), sqrt(pi/s)-pi*sqrt(b)*exp(b*s)*erfc(sqrt(b*s)), Abs(arg(b)) < pi, S.Zero, dco), # 4.2.22 (1/(a*sqrt(t) + t**(3/2)), pi*a**(S(1)/2)*exp(a*s)*erfc(sqrt(a*s)), S.true, S.Zero, dco), # Not in Bateman54 (t**n, gamma(n+1)/s**(n+1), n > -1, S.Zero, dco), # 4.3.1 ((a*t+b)**n, uppergamma(n+1, b/a*s)*exp(-b/a*s)/s**(n+1)/a, And(n > -1, Abs(arg(b/a)) < pi), S.Zero, dco), # 4.3.4 (t**n/(t+a), a**n*gamma(n+1)*uppergamma(-n, a*s), And(n > -1, Abs(arg(a)) < pi), S.Zero, dco), # 4.3.7 (exp(a*t-tau), exp(-tau)/(s-a), S.true, re(a), dco), # 4.5.1 (t*exp(a*t-tau), exp(-tau)/(s-a)**2, S.true, re(a), dco), # 4.5.2 (t**n*exp(a*t), gamma(n+1)/(s-a)**(n+1), re(n) > -1, re(a), dco), # 4.5.3 (exp(-a*t**2), sqrt(pi/4/a)*exp(s**2/4/a)*erfc(s/sqrt(4*a)), re(a) > 0, S.Zero, dco), # 4.5.21 (t*exp(-a*t**2), 1/(2*a)-2/sqrt(pi)/(4*a)**(S(3)/2)*s*erfc(s/sqrt(4*a)), re(a) > 0, S.Zero, dco), # 4.5.22 (exp(-a/t), 2*sqrt(a/s)*besselk(1, 2*sqrt(a*s)), re(a) >= 0, S.Zero, dco), # 4.5.25 (sqrt(t)*exp(-a/t), S(1)/2*sqrt(pi/s**3)*(1+2*sqrt(a*s))*exp(-2*sqrt(a*s)), re(a) >= 0, S.Zero, dco), # 4.5.26 (exp(-a/t)/sqrt(t), sqrt(pi/s)*exp(-2*sqrt(a*s)), re(a) >= 0, S.Zero, dco), # 4.5.27 (exp(-a/t)/(t*sqrt(t)), sqrt(pi/a)*exp(-2*sqrt(a*s)), re(a) > 0, S.Zero, dco), # 4.5.28 (t**n*exp(-a/t), 2*(a/s)**((n+1)/2)*besselk(n+1, 2*sqrt(a*s)), re(a) > 0, S.Zero, dco), # 4.5.29 (exp(-2*sqrt(a*t)), s**(-1)-sqrt(pi*a)*s**(-S(3)/2)*exp(a/s) * erfc(sqrt(a/s)), Abs(arg(a)) < pi, S.Zero, dco), # 4.5.31 (exp(-2*sqrt(a*t))/sqrt(t), (pi/s)**(S(1)/2)*exp(a/s)*erfc(sqrt(a/s)), Abs(arg(a)) < pi, S.Zero, dco), # 4.5.33 (exp(-a*exp(-t)), a**(-s)*lowergamma(s, a), S.true, S.Zero, dco), # 4.5.36 (exp(-a*exp(t)), a**s*uppergamma(-s, a), re(a) > 0, S.Zero, dco), # 4.5.37 (log(a*t), -log(exp(S.EulerGamma)*s/a)/s, a > 0, S.Zero, dco), # 4.6.1 (log(1+a*t), -exp(s/a)/s*Ei(-s/a), Abs(arg(a)) < pi, S.Zero, dco), # 4.6.4 (log(a*t+b), (log(b)-exp(s/b/a)/s*a*Ei(-s/b))/s*a, And(a > 0, Abs(arg(b)) < pi), S.Zero, dco), # 4.6.5 (log(t)/sqrt(t), -sqrt(pi/s)*log(4*s*exp(S.EulerGamma)), S.true, S.Zero, dco), # 4.6.9 (t**n*log(t), gamma(n+1)*s**(-n-1)*(digamma(n+1)-log(s)), re(n) > -1, S.Zero, dco), # 4.6.11 (log(a*t)**2, (log(exp(S.EulerGamma)*s/a)**2+pi**2/6)/s, a > 0, S.Zero, dco), # 4.6.13 (sin(omega*t), omega/(s**2+omega**2), S.true, Abs(im(omega)), dco), # 4,7,1 (Abs(sin(omega*t)), omega/(s**2+omega**2)*coth(pi*s/2/omega), omega > 0, S.Zero, dco), # 4.7.2 (sin(omega*t)/t, atan(omega/s), S.true, Abs(im(omega)), dco), # 4.7.16 (sin(omega*t)**2/t, log(1+4*omega**2/s**2)/4, S.true, 2*Abs(im(omega)), dco), # 4.7.17 (sin(omega*t)**2/t**2, omega*atan(2*omega/s)-s*log(1+4*omega**2/s**2)/4, S.true, 2*Abs(im(omega)), dco), # 4.7.20 (sin(2*sqrt(a*t)), sqrt(pi*a)/s/sqrt(s)*exp(-a/s), S.true, S.Zero, dco), # 4.7.32 (sin(2*sqrt(a*t))/t, pi*erf(sqrt(a/s)), S.true, S.Zero, dco), # 4.7.34 (cos(omega*t), s/(s**2+omega**2), S.true, Abs(im(omega)), dco), # 4.7.43 (cos(omega*t)**2, (s**2+2*omega**2)/(s**2+4*omega**2)/s, S.true, 2*Abs(im(omega)), dco), # 4.7.45 (sqrt(t)*cos(2*sqrt(a*t)), sqrt(pi)/2*s**(-S(5)/2)*(s-2*a)*exp(-a/s), S.true, S.Zero, dco), # 4.7.66 (cos(2*sqrt(a*t))/sqrt(t), sqrt(pi/s)*exp(-a/s), S.true, S.Zero, dco), # 4.7.67 (sin(a*t)*sin(b*t), 2*a*b*s/(s**2+(a+b)**2)/(s**2+(a-b)**2), S.true, Abs(im(a))+Abs(im(b)), dco), # 4.7.78 (cos(a*t)*sin(b*t), b*(s**2-a**2+b**2)/(s**2+(a+b)**2)/(s**2+(a-b)**2), S.true, Abs(im(a))+Abs(im(b)), dco), # 4.7.79 (cos(a*t)*cos(b*t), s*(s**2+a**2+b**2)/(s**2+(a+b)**2)/(s**2+(a-b)**2), S.true, Abs(im(a))+Abs(im(b)), dco), # 4.7.80 (sinh(a*t), a/(s**2-a**2), S.true, Abs(re(a)), dco), # 4.9.1 (cosh(a*t), s/(s**2-a**2), S.true, Abs(re(a)), dco), # 4.9.2 (sinh(a*t)**2, 2*a**2/(s**3-4*a**2*s), S.true, 2*Abs(re(a)), dco), # 4.9.3 (cosh(a*t)**2, (s**2-2*a**2)/(s**3-4*a**2*s), S.true, 2*Abs(re(a)), dco), # 4.9.4 (sinh(a*t)/t, log((s+a)/(s-a))/2, S.true, Abs(re(a)), dco), # 4.9.12 (t**n*sinh(a*t), gamma(n+1)/2*((s-a)**(-n-1)-(s+a)**(-n-1)), n > -2, Abs(a), dco), # 4.9.18 (t**n*cosh(a*t), gamma(n+1)/2*((s-a)**(-n-1)+(s+a)**(-n-1)), n > -1, Abs(a), dco), # 4.9.19 (sinh(2*sqrt(a*t)), sqrt(pi*a)/s/sqrt(s)*exp(a/s), S.true, S.Zero, dco), # 4.9.34 (cosh(2*sqrt(a*t)), 1/s+sqrt(pi*a)/s/sqrt(s)*exp(a/s)*erf(sqrt(a/s)), S.true, S.Zero, dco), # 4.9.35 ( sqrt(t)*sinh(2*sqrt(a*t)), pi**(S(1)/2)*s**(-S(5)/2)*(s/2+a) * exp(a/s)*erf(sqrt(a/s))-a**(S(1)/2)*s**(-2), S.true, S.Zero, dco), # 4.9.36 (sqrt(t)*cosh(2*sqrt(a*t)), pi**(S(1)/2)*s**(-S(5)/2)*(s/2+a)*exp(a/s), S.true, S.Zero, dco), # 4.9.37 (sinh(2*sqrt(a*t))/sqrt(t), pi**(S(1)/2)*s**(-S(1)/2)*exp(a/s) * erf(sqrt(a/s)), S.true, S.Zero, dco), # 4.9.38 (cosh(2*sqrt(a*t))/sqrt(t), pi**(S(1)/2)*s**(-S(1)/2)*exp(a/s), S.true, S.Zero, dco), # 4.9.39 (sinh(sqrt(a*t))**2/sqrt(t), pi**(S(1)/2)/2*s**(-S(1)/2)*(exp(a/s)-1), S.true, S.Zero, dco), # 4.9.40 (cosh(sqrt(a*t))**2/sqrt(t), pi**(S(1)/2)/2*s**(-S(1)/2)*(exp(a/s)+1), S.true, S.Zero, dco), # 4.9.41 (erf(a*t), exp(s**2/(2*a)**2)*erfc(s/(2*a))/s, 4*Abs(arg(a)) < pi, S.Zero, dco), # 4.12.2 (erf(sqrt(a*t)), sqrt(a)/sqrt(s+a)/s, S.true, Max(S.Zero, -re(a)), dco), # 4.12.4 (exp(a*t)*erf(sqrt(a*t)), sqrt(a)/sqrt(s)/(s-a), S.true, Max(S.Zero, re(a)), dco), # 4.12.5 (erf(sqrt(a/t)/2), (1-exp(-sqrt(a*s)))/s, re(a) > 0, S.Zero, dco), # 4.12.6 (erfc(sqrt(a*t)), (sqrt(s+a)-sqrt(a))/sqrt(s+a)/s, S.true, -re(a), dco), # 4.12.9 (exp(a*t)*erfc(sqrt(a*t)), 1/(s+sqrt(a*s)), S.true, S.Zero, dco), # 4.12.10 (erfc(sqrt(a/t)/2), exp(-sqrt(a*s))/s, re(a) > 0, S.Zero, dco), # 4.2.11 (besselj(n, a*t), a**n/(sqrt(s**2+a**2)*(s+sqrt(s**2+a**2))**n), re(n) > -1, Abs(im(a)), dco), # 4.14.1 (t**b*besselj(n, a*t), 2**n/sqrt(pi)*gamma(n+S.Half)*a**n*(s**2+a**2)**(-n-S.Half), And(re(n) > -S.Half, Eq(b, n)), Abs(im(a)), dco), # 4.14.7 (t**b*besselj(n, a*t), 2**(n+1)/sqrt(pi)*gamma(n+S(3)/2)*a**n*s*(s**2+a**2)**(-n-S(3)/2), And(re(n) > -1, Eq(b, n+1)), Abs(im(a)), dco), # 4.14.8 (besselj(0, 2*sqrt(a*t)), exp(-a/s)/s, S.true, S.Zero, dco), # 4.14.25 (t**(b)*besselj(n, 2*sqrt(a*t)), a**(n/2)*s**(-n-1)*exp(-a/s), And(re(n) > -1, Eq(b, n*S.Half)), S.Zero, dco), # 4.14.30 (besselj(0, a*sqrt(t**2+b*t)), exp(b*s-b*sqrt(s**2+a**2))/sqrt(s**2+a**2), Abs(arg(b)) < pi, Abs(im(a)), dco), # 4.15.19 (besseli(n, a*t), a**n/(sqrt(s**2-a**2)*(s+sqrt(s**2-a**2))**n), re(n) > -1, Abs(re(a)), dco), # 4.16.1 (t**b*besseli(n, a*t), 2**n/sqrt(pi)*gamma(n+S.Half)*a**n*(s**2-a**2)**(-n-S.Half), And(re(n) > -S.Half, Eq(b, n)), Abs(re(a)), dco), # 4.16.6 (t**b*besseli(n, a*t), 2**(n+1)/sqrt(pi)*gamma(n+S(3)/2)*a**n*s*(s**2-a**2)**(-n-S(3)/2), And(re(n) > -1, Eq(b, n+1)), Abs(re(a)), dco), # 4.16.7 (t**(b)*besseli(n, 2*sqrt(a*t)), a**(n/2)*s**(-n-1)*exp(a/s), And(re(n) > -1, Eq(b, n*S.Half)), S.Zero, dco), # 4.16.18 (bessely(0, a*t), -2/pi*asinh(s/a)/sqrt(s**2+a**2), S.true, Abs(im(a)), dco), # 4.15.44 (besselk(0, a*t), log((s + sqrt(s**2-a**2))/a)/(sqrt(s**2-a**2)), S.true, -re(a), dco) # 4.16.23 ] return laplace_transform_rules, t, s @DEBUG_WRAP def _laplace_rule_timescale(f, t, s): """ This function applies the time-scaling rule of the Laplace transform in a straight-forward way. For example, if it gets ``(f(a*t), t, s)``, it will compute ``LaplaceTransform(f(t)/a, t, s/a)`` if ``a>0``. """ a = Wild('a', exclude=[t]) g = WildFunction('g', nargs=1) ma1 = f.match(g) if ma1: arg = ma1[g].args[0].collect(t) ma2 = arg.match(a*t) if ma2 and ma2[a].is_positive and ma2[a] != 1: _debug(' rule: time scaling (4.1.4)') r, pr, cr = _laplace_transform( 1/ma2[a]*ma1[g].func(t), t, s/ma2[a], simplify=False) return (r, pr, cr) return None @DEBUG_WRAP def _laplace_rule_heaviside(f, t, s): """ This function deals with time-shifted Heaviside step functions. If the time shift is positive, it applies the time-shift rule of the Laplace transform. For example, if it gets ``(Heaviside(t-a)*f(t), t, s)``, it will compute ``exp(-a*s)*LaplaceTransform(f(t+a), t, s)``. If the time shift is negative, the Heaviside function is simply removed as it means nothing to the Laplace transform. The function does not remove a factor ``Heaviside(t)``; this is done by the simple rules. """ a = Wild('a', exclude=[t]) y = Wild('y') g = Wild('g') if ma1 := f.match(Heaviside(y) * g): if ma2 := ma1[y].match(t - a): if ma2[a].is_positive: _debug(' rule: time shift (4.1.4)') r, pr, cr = _laplace_transform( ma1[g].subs(t, t + ma2[a]), t, s, simplify=False) return (exp(-ma2[a] * s) * r, pr, cr) if ma2[a].is_negative: _debug( ' rule: Heaviside factor; negative time shift (4.1.4)') r, pr, cr = _laplace_transform(ma1[g], t, s, simplify=False) return (r, pr, cr) if ma2 := ma1[y].match(a - t): if ma2[a].is_positive: _debug(' rule: Heaviside window open') r, pr, cr = _laplace_transform( (1 - Heaviside(t - ma2[a])) * ma1[g], t, s, simplify=False) return (r, pr, cr) if ma2[a].is_negative: _debug(' rule: Heaviside window closed') return (0, 0, S.true) return None @DEBUG_WRAP def _laplace_rule_exp(f, t, s): """ If this function finds a factor ``exp(a*t)``, it applies the frequency-shift rule of the Laplace transform and adjusts the convergence plane accordingly. For example, if it gets ``(exp(-a*t)*f(t), t, s)``, it will compute ``LaplaceTransform(f(t), t, s+a)``. """ a = Wild('a', exclude=[t]) y = Wild('y') z = Wild('z') ma1 = f.match(exp(y)*z) if ma1: ma2 = ma1[y].collect(t).match(a*t) if ma2: _debug(' rule: multiply with exp (4.1.5)') r, pr, cr = _laplace_transform(ma1[z], t, s-ma2[a], simplify=False) return (r, pr+re(ma2[a]), cr) return None @DEBUG_WRAP def _laplace_rule_delta(f, t, s): """ If this function finds a factor ``DiracDelta(b*t-a)``, it applies the masking property of the delta distribution. For example, if it gets ``(DiracDelta(t-a)*f(t), t, s)``, it will return ``(f(a)*exp(-a*s), -a, True)``. """ # This rule is not in Bateman54 a = Wild('a', exclude=[t]) b = Wild('b', exclude=[t]) y = Wild('y') z = Wild('z') ma1 = f.match(DiracDelta(y)*z) if ma1 and not ma1[z].has(DiracDelta): ma2 = ma1[y].collect(t).match(b*t-a) if ma2: _debug(' rule: multiply with DiracDelta') loc = ma2[a]/ma2[b] if re(loc) >= 0 and im(loc) == 0: fn = exp(-ma2[a]/ma2[b]*s)*ma1[z] if fn.has(sin, cos): # Then it may be possible that a sinc() is present in the # term; let's try this: fn = fn.rewrite(sinc).ratsimp() n, d = [x.subs(t, ma2[a]/ma2[b]) for x in fn.as_numer_denom()] if d != 0: return (n/d/ma2[b], S.NegativeInfinity, S.true) else: return None else: return (0, S.NegativeInfinity, S.true) if ma1[y].is_polynomial(t): ro = roots(ma1[y], t) if ro != {} and set(ro.values()) == {1}: slope = diff(ma1[y], t) r = Add( *[exp(-x*s)*ma1[z].subs(t, s)/slope.subs(t, x) for x in list(ro.keys()) if im(x) == 0 and re(x) >= 0]) return (r, S.NegativeInfinity, S.true) return None @DEBUG_WRAP def _laplace_trig_split(fn): """ Helper function for `_laplace_rule_trig`. This function returns two terms `f` and `g`. `f` contains all product terms with sin, cos, sinh, cosh in them; `g` contains everything else. """ trigs = [S.One] other = [S.One] for term in Mul.make_args(fn): if term.has(sin, cos, sinh, cosh, exp): trigs.append(term) else: other.append(term) f = Mul(*trigs) g = Mul(*other) return f, g @DEBUG_WRAP def _laplace_trig_expsum(f, t): """ Helper function for `_laplace_rule_trig`. This function expects the `f` from `_laplace_trig_split`. It returns two lists `xm` and `xn`. `xm` is a list of dictionaries with keys `k` and `a` representing a function `k*exp(a*t)`. `xn` is a list of all terms that cannot be brought into that form, which may happen, e.g., when a trigonometric function has another function in its argument. """ c1 = Wild('c1', exclude=[t]) c0 = Wild('c0', exclude=[t]) p = Wild('p', exclude=[t]) xm = [] xn = [] x1 = f.rewrite(exp).expand() for term in Add.make_args(x1): if not term.has(t): xm.append({'k': term, 'a': 0, re: 0, im: 0}) continue term = _laplace_deep_collect(term.powsimp(combine='exp'), t) if (r := term.match(p*exp(c1*t+c0))) is not None: xm.append({ 'k': r[p]*exp(r[c0]), 'a': r[c1], re: re(r[c1]), im: im(r[c1])}) else: xn.append(term) return xm, xn @DEBUG_WRAP def _laplace_trig_ltex(xm, t, s): """ Helper function for `_laplace_rule_trig`. This function takes the list of exponentials `xm` from `_laplace_trig_expsum` and simplifies complex conjugate and real symmetric poles. It returns the result as a sum and the convergence plane. """ results = [] planes = [] def _simpc(coeffs): nc = coeffs.copy() for k in range(len(nc)): ri = nc[k].as_real_imag() if ri[0].has(im): nc[k] = nc[k].rewrite(cos) else: nc[k] = (ri[0] + I*ri[1]).rewrite(cos) return nc def _quadpole(t1, k1, k2, k3, s): a, k0, a_r, a_i = t1['a'], t1['k'], t1[re], t1[im] nc = [ k0 + k1 + k2 + k3, a*(k0 + k1 - k2 - k3) - 2*I*a_i*k1 + 2*I*a_i*k2, ( a**2*(-k0 - k1 - k2 - k3) + a*(4*I*a_i*k0 + 4*I*a_i*k3) + 4*a_i**2*k0 + 4*a_i**2*k3), ( a**3*(-k0 - k1 + k2 + k3) + a**2*(4*I*a_i*k0 + 2*I*a_i*k1 - 2*I*a_i*k2 - 4*I*a_i*k3) + a*(4*a_i**2*k0 - 4*a_i**2*k3)) ] dc = [ S.One, S.Zero, 2*a_i**2 - 2*a_r**2, S.Zero, a_i**4 + 2*a_i**2*a_r**2 + a_r**4] n = Add( *[x*s**y for x, y in zip(_simpc(nc), range(len(nc))[::-1])]) d = Add( *[x*s**y for x, y in zip(dc, range(len(dc))[::-1])]) return n/d def _ccpole(t1, k1, s): a, k0, a_r, a_i = t1['a'], t1['k'], t1[re], t1[im] nc = [k0 + k1, -a*k0 - a*k1 + 2*I*a_i*k0] dc = [S.One, -2*a_r, a_i**2 + a_r**2] n = Add( *[x*s**y for x, y in zip(_simpc(nc), range(len(nc))[::-1])]) d = Add( *[x*s**y for x, y in zip(dc, range(len(dc))[::-1])]) return n/d def _rspole(t1, k2, s): a, k0, a_r, a_i = t1['a'], t1['k'], t1[re], t1[im] nc = [k0 + k2, a*k0 - a*k2 - 2*I*a_i*k0] dc = [S.One, -2*I*a_i, -a_i**2 - a_r**2] n = Add( *[x*s**y for x, y in zip(_simpc(nc), range(len(nc))[::-1])]) d = Add( *[x*s**y for x, y in zip(dc, range(len(dc))[::-1])]) return n/d def _sypole(t1, k3, s): a, k0 = t1['a'], t1['k'] nc = [k0 + k3, a*(k0 - k3)] dc = [S.One, S.Zero, -a**2] n = Add( *[x*s**y for x, y in zip(_simpc(nc), range(len(nc))[::-1])]) d = Add( *[x*s**y for x, y in zip(dc, range(len(dc))[::-1])]) return n/d def _simplepole(t1, s): a, k0 = t1['a'], t1['k'] n = k0 d = s - a return n/d while len(xm) > 0: t1 = xm.pop() i_imagsym = None i_realsym = None i_pointsym = None # The following code checks all remaining poles. If t1 is a pole at # a+b*I, then we check for a-b*I, -a+b*I, and -a-b*I, and # assign the respective indices to i_imagsym, i_realsym, i_pointsym. # -a-b*I / i_pointsym only applies if both a and b are != 0. for i in range(len(xm)): real_eq = t1[re] == xm[i][re] realsym = t1[re] == -xm[i][re] imag_eq = t1[im] == xm[i][im] imagsym = t1[im] == -xm[i][im] if realsym and imagsym and t1[re] != 0 and t1[im] != 0: i_pointsym = i elif realsym and imag_eq and t1[re] != 0: i_realsym = i elif real_eq and imagsym and t1[im] != 0: i_imagsym = i # The next part looks for four possible pole constellations: # quad: a+b*I, a-b*I, -a+b*I, -a-b*I # cc: a+b*I, a-b*I (a may be zero) # quad: a+b*I, -a+b*I (b may be zero) # point: a+b*I, -a-b*I (a!=0 and b!=0 is needed, but that has been # asserted when finding i_pointsym above.) # If none apply, then t1 is a simple pole. if ( i_imagsym is not None and i_realsym is not None and i_pointsym is not None): results.append( _quadpole(t1, xm[i_imagsym]['k'], xm[i_realsym]['k'], xm[i_pointsym]['k'], s)) planes.append(Abs(re(t1['a']))) # The three additional poles have now been used; to pop them # easily we have to do it from the back. indices_to_pop = [i_imagsym, i_realsym, i_pointsym] indices_to_pop.sort(reverse=True) for i in indices_to_pop: xm.pop(i) elif i_imagsym is not None: results.append(_ccpole(t1, xm[i_imagsym]['k'], s)) planes.append(t1[re]) xm.pop(i_imagsym) elif i_realsym is not None: results.append(_rspole(t1, xm[i_realsym]['k'], s)) planes.append(Abs(t1[re])) xm.pop(i_realsym) elif i_pointsym is not None: results.append(_sypole(t1, xm[i_pointsym]['k'], s)) planes.append(Abs(t1[re])) xm.pop(i_pointsym) else: results.append(_simplepole(t1, s)) planes.append(t1[re]) return Add(*results), Max(*planes) @DEBUG_WRAP def _laplace_rule_trig(fn, t_, s): """ This rule covers trigonometric factors by splitting everything into a sum of exponential functions and collecting complex conjugate poles and real symmetric poles. """ t = Dummy('t', real=True) if not fn.has(sin, cos, sinh, cosh): return None f, g = _laplace_trig_split(fn.subs(t_, t)) xm, xn = _laplace_trig_expsum(f, t) if len(xn) > 0: # TODO not implemented yet, but also not important return None if not g.has(t): r, p = _laplace_trig_ltex(xm, t, s) return g*r, p, S.true else: # Just transform `g` and make frequency-shifted copies planes = [] results = [] G, G_plane, G_cond = _laplace_transform(g, t, s, simplify=False) for x1 in xm: results.append(x1['k']*G.subs(s, s-x1['a'])) planes.append(G_plane+re(x1['a'])) return Add(*results).subs(t, t_), Max(*planes), G_cond @DEBUG_WRAP def _laplace_rule_diff(f, t, s): """ This function looks for derivatives in the time domain and replaces it by factors of `s` and initial conditions in the frequency domain. For example, if it gets ``(diff(f(t), t), t, s)``, it will compute ``s*LaplaceTransform(f(t), t, s) - f(0)``. """ a = Wild('a', exclude=[t]) n = Wild('n', exclude=[t]) g = WildFunction('g') ma1 = f.match(a*Derivative(g, (t, n))) if ma1 and ma1[n].is_integer: m = [z.has(t) for z in ma1[g].args] if sum(m) == 1: _debug(' rule: time derivative (4.1.8)') d = [] for k in range(ma1[n]): if k == 0: y = ma1[g].subs(t, 0) else: y = Derivative(ma1[g], (t, k)).subs(t, 0) d.append(s**(ma1[n]-k-1)*y) r, pr, cr = _laplace_transform(ma1[g], t, s, simplify=False) return (ma1[a]*(s**ma1[n]*r - Add(*d)), pr, cr) return None @DEBUG_WRAP def _laplace_rule_sdiff(f, t, s): """ This function looks for multiplications with polynoimials in `t` as they correspond to differentiation in the frequency domain. For example, if it gets ``(t*f(t), t, s)``, it will compute ``-Derivative(LaplaceTransform(f(t), t, s), s)``. """ if f.is_Mul: pfac = [1] ofac = [1] for fac in Mul.make_args(f): if fac.is_polynomial(t): pfac.append(fac) else: ofac.append(fac) if len(pfac) > 1: pex = prod(pfac) pc = Poly(pex, t).all_coeffs() N = len(pc) if N > 1: oex = prod(ofac) r_, p_, c_ = _laplace_transform(oex, t, s, simplify=False) deri = [r_] d1 = False try: d1 = -diff(deri[-1], s) except ValueError: d1 = False if r_.has(LaplaceTransform): for k in range(N-1): deri.append((-1)**(k+1)*Derivative(r_, s, k+1)) elif d1: deri.append(d1) for k in range(N-2): deri.append(-diff(deri[-1], s)) if d1: r = Add(*[pc[N-n-1]*deri[n] for n in range(N)]) return (r, p_, c_) # We still have to cover the possibility that there is a symbolic positive # integer exponent. n = Wild('n', exclude=[t]) g = Wild('g') if ma1 := f.match(t**n*g): if ma1[n].is_integer and ma1[n].is_positive: r_, p_, c_ = _laplace_transform(ma1[g], t, s, simplify=False) return (-1)**ma1[n]*diff(r_, (s, ma1[n])), p_, c_ return None @DEBUG_WRAP def _laplace_expand(f, t, s): """ This function tries to expand its argument with successively stronger methods: first it will expand on the top level, then it will expand any multiplications in depth, then it will try all avilable expansion methods, and finally it will try to expand trigonometric functions. If it can expand, it will then compute the Laplace transform of the expanded term. """ r = expand(f, deep=False) if r.is_Add: return _laplace_transform(r, t, s, simplify=False) r = expand_mul(f) if r.is_Add: return _laplace_transform(r, t, s, simplify=False) r = expand(f) if r.is_Add: return _laplace_transform(r, t, s, simplify=False) if r != f: return _laplace_transform(r, t, s, simplify=False) r = expand(expand_trig(f)) if r.is_Add: return _laplace_transform(r, t, s, simplify=False) return None @DEBUG_WRAP def _laplace_apply_prog_rules(f, t, s): """ This function applies all program rules and returns the result if one of them gives a result. """ prog_rules = [_laplace_rule_heaviside, _laplace_rule_delta, _laplace_rule_timescale, _laplace_rule_exp, _laplace_rule_trig, _laplace_rule_diff, _laplace_rule_sdiff] for p_rule in prog_rules: if (L := p_rule(f, t, s)) is not None: return L return None @DEBUG_WRAP def _laplace_apply_simple_rules(f, t, s): """ This function applies all simple rules and returns the result if one of them gives a result. """ simple_rules, t_, s_ = _laplace_build_rules() prep_old = '' prep_f = '' for t_dom, s_dom, check, plane, prep in simple_rules: if prep_old != prep: prep_f = prep(f.subs({t: t_})) prep_old = prep ma = prep_f.match(t_dom) if ma: try: c = check.xreplace(ma) except TypeError: # This may happen if the time function has imaginary # numbers in it. Then we give up. continue if c == S.true: return (s_dom.xreplace(ma).subs({s_: s}), plane.xreplace(ma), S.true) return None @DEBUG_WRAP def _piecewise_to_heaviside(f, t): """ This function converts a Piecewise expression to an expression written with Heaviside. It is not exact, but valid in the context of the Laplace transform. """ if not t.is_real: r = Dummy('r', real=True) return _piecewise_to_heaviside(f.xreplace({t: r}), r).xreplace({r: t}) x = piecewise_exclusive(f) r = [] for fn, cond in x.args: # Here we do not need to do many checks because piecewise_exclusive # has a clearly predictable output. However, if any of the conditions # is not relative to t, this function just returns the input argument. if isinstance(cond, Relational) and t in cond.args: if isinstance(cond, (Eq, Ne)): # We do not cover this case; these would be single-point # exceptions that do not play a role in Laplace practice, # except if they contain Dirac impulses, and then we can # expect users to not try to use Piecewise for writing it. return f else: r.append(Heaviside(cond.gts - cond.lts)*fn) elif isinstance(cond, Or) and len(cond.args) == 2: # Or(t<2, t>4), Or(t>4, t<=2), ... in any order with any <= >= for c2 in cond.args: if c2.lhs == t: r.append(Heaviside(c2.gts - c2.lts)*fn) else: return f elif isinstance(cond, And) and len(cond.args) == 2: # And(t>2, t<4), And(t>4, t<=2), ... in any order with any <= >= c0, c1 = cond.args if c0.lhs == t and c1.lhs == t: if '>' in c0.rel_op: c0, c1 = c1, c0 r.append( (Heaviside(c1.gts - c1.lts) - Heaviside(c0.lts - c0.gts))*fn) else: return f else: return f return Add(*r) def laplace_correspondence(f, fdict, /): """ This helper function takes a function `f` that is the result of a ``laplace_transform`` or an ``inverse_laplace_transform``. It replaces all unevaluated ``LaplaceTransform(y(t), t, s)`` by `Y(s)` for any `s` and all ``InverseLaplaceTransform(Y(s), s, t)`` by `y(t)` for any `t` if ``fdict`` contains a correspondence ``{y: Y}``. Parameters ========== f : sympy expression Expression containing unevaluated ``LaplaceTransform`` or ``LaplaceTransform`` objects. fdict : dictionary Dictionary containing one or more function correspondences, e.g., ``{x: X, y: Y}`` meaning that ``X`` and ``Y`` are the Laplace transforms of ``x`` and ``y``, respectively. Examples ======== >>> from sympy import laplace_transform, diff, Function >>> from sympy import laplace_correspondence, inverse_laplace_transform >>> from sympy.abc import t, s >>> y = Function("y") >>> Y = Function("Y") >>> z = Function("z") >>> Z = Function("Z") >>> f = laplace_transform(diff(y(t), t, 1) + z(t), t, s, noconds=True) >>> laplace_correspondence(f, {y: Y, z: Z}) s*Y(s) + Z(s) - y(0) >>> f = inverse_laplace_transform(Y(s), s, t) >>> laplace_correspondence(f, {y: Y}) y(t) """ p = Wild('p') s = Wild('s') t = Wild('t') a = Wild('a') if ( not isinstance(f, Expr) or (not f.has(LaplaceTransform) and not f.has(InverseLaplaceTransform))): return f for y, Y in fdict.items(): if ( (m := f.match(LaplaceTransform(y(a), t, s))) is not None and m[a] == m[t]): return Y(m[s]) if ( (m := f.match(InverseLaplaceTransform(Y(a), s, t, p))) is not None and m[a] == m[s]): return y(m[t]) func = f.func args = [laplace_correspondence(arg, fdict) for arg in f.args] return func(*args) def laplace_initial_conds(f, t, fdict, /): """ This helper function takes a function `f` that is the result of a ``laplace_transform``. It takes an fdict of the form ``{y: [1, 4, 2]}``, where the values in the list are the initial value, the initial slope, the initial second derivative, etc., of the function `y(t)`, and replaces all unevaluated initial conditions. Parameters ========== f : sympy expression Expression containing initial conditions of unevaluated functions. t : sympy expression Variable for which the initial conditions are to be applied. fdict : dictionary Dictionary containing a list of initial conditions for every function, e.g., ``{y: [0, 1, 2], x: [3, 4, 5]}``. The order of derivatives is ascending, so `0`, `1`, `2` are `y(0)`, `y'(0)`, and `y''(0)`, respectively. Examples ======== >>> from sympy import laplace_transform, diff, Function >>> from sympy import laplace_correspondence, laplace_initial_conds >>> from sympy.abc import t, s >>> y = Function("y") >>> Y = Function("Y") >>> f = laplace_transform(diff(y(t), t, 3), t, s, noconds=True) >>> g = laplace_correspondence(f, {y: Y}) >>> laplace_initial_conds(g, t, {y: [2, 4, 8, 16, 32]}) s**3*Y(s) - 2*s**2 - 4*s - 8 """ for y, ic in fdict.items(): for k in range(len(ic)): if k == 0: f = f.replace(y(0), ic[0]) elif k == 1: f = f.replace(Subs(Derivative(y(t), t), t, 0), ic[1]) else: f = f.replace(Subs(Derivative(y(t), (t, k)), t, 0), ic[k]) return f @DEBUG_WRAP def _laplace_transform(fn, t_, s_, *, simplify): """ Front-end function of the Laplace transform. It tries to apply all known rules recursively, and if everything else fails, it tries to integrate. """ terms_t = Add.make_args(fn) terms_s = [] terms = [] planes = [] conditions = [] for ff in terms_t: k, ft = ff.as_independent(t_, as_Add=False) if ft.has(SingularityFunction): _terms = Add.make_args(ft.rewrite(Heaviside)) for _term in _terms: k1, f1 = _term.as_independent(t_, as_Add=False) terms.append((k*k1, f1)) elif ft.func == Piecewise and not ft.has(DiracDelta(t_)): _terms = Add.make_args(_piecewise_to_heaviside(ft, t_)) for _term in _terms: k1, f1 = _term.as_independent(t_, as_Add=False) terms.append((k*k1, f1)) else: terms.append((k, ft)) for k, ft in terms: if ft.has(SingularityFunction): r = (LaplaceTransform(ft, t_, s_), S.NegativeInfinity, True) else: if ft.has(Heaviside(t_)) and not ft.has(DiracDelta(t_)): # For t>=0, Heaviside(t)=1 can be used, except if there is also # a DiracDelta(t) present, in which case removing Heaviside(t) # is unnecessary because _laplace_rule_delta can deal with it. ft = ft.subs(Heaviside(t_), 1) if ( (r := _laplace_apply_simple_rules(ft, t_, s_)) is not None or (r := _laplace_apply_prog_rules(ft, t_, s_)) is not None or (r := _laplace_expand(ft, t_, s_)) is not None): pass elif any(undef.has(t_) for undef in ft.atoms(AppliedUndef)): # If there are undefined functions f(t) then integration is # unlikely to do anything useful so we skip it and given an # unevaluated LaplaceTransform. r = (LaplaceTransform(ft, t_, s_), S.NegativeInfinity, True) elif (r := _laplace_transform_integration( ft, t_, s_, simplify=simplify)) is not None: pass else: r = (LaplaceTransform(ft, t_, s_), S.NegativeInfinity, True) (ri_, pi_, ci_) = r terms_s.append(k*ri_) planes.append(pi_) conditions.append(ci_) result = Add(*terms_s) if simplify: result = result.simplify(doit=False) plane = Max(*planes) condition = And(*conditions) return result, plane, condition class LaplaceTransform(IntegralTransform): """ Class representing unevaluated Laplace transforms. For usage of this class, see the :class:`IntegralTransform` docstring. For how to compute Laplace transforms, see the :func:`laplace_transform` docstring. If this is called with ``.doit()``, it returns the Laplace transform as an expression. If it is called with ``.doit(noconds=False)``, it returns a tuple containing the same expression, a convergence plane, and conditions. """ _name = 'Laplace' def _compute_transform(self, f, t, s, **hints): _simplify = hints.get('simplify', False) LT = _laplace_transform_integration(f, t, s, simplify=_simplify) return LT def _as_integral(self, f, t, s): return Integral(f*exp(-s*t), (t, S.Zero, S.Infinity)) def doit(self, **hints): """ Try to evaluate the transform in closed form. Explanation =========== Standard hints are the following: - ``noconds``: if True, do not return convergence conditions. The default setting is `True`. - ``simplify``: if True, it simplifies the final result. The default setting is `False`. """ _noconds = hints.get('noconds', True) _simplify = hints.get('simplify', False) debugf('[LT doit] (%s, %s, %s)', (self.function, self.function_variable, self.transform_variable)) t_ = self.function_variable s_ = self.transform_variable fn = self.function r = _laplace_transform(fn, t_, s_, simplify=_simplify) if _noconds: return r[0] else: return r def laplace_transform(f, t, s, legacy_matrix=True, **hints): r""" Compute the Laplace Transform `F(s)` of `f(t)`, .. math :: F(s) = \int_{0^{-}}^\infty e^{-st} f(t) \mathrm{d}t. Explanation =========== For all sensible functions, this converges absolutely in a half-plane .. math :: a < \operatorname{Re}(s) This function returns ``(F, a, cond)`` where ``F`` is the Laplace transform of ``f``, `a` is the half-plane of convergence, and `cond` are auxiliary convergence conditions. The implementation is rule-based, and if you are interested in which rules are applied, and whether integration is attempted, you can switch debug information on by setting ``sympy.SYMPY_DEBUG=True``. The numbers of the rules in the debug information (and the code) refer to Bateman's Tables of Integral Transforms [1]. The lower bound is `0-`, meaning that this bound should be approached from the lower side. This is only necessary if distributions are involved. At present, it is only done if `f(t)` contains ``DiracDelta``, in which case the Laplace transform is computed implicitly as .. math :: F(s) = \lim_{\tau\to 0^{-}} \int_{\tau}^\infty e^{-st} f(t) \mathrm{d}t by applying rules. If the Laplace transform cannot be fully computed in closed form, this function returns expressions containing unevaluated :class:`LaplaceTransform` objects. For a description of possible hints, refer to the docstring of :func:`sympy.integrals.transforms.IntegralTransform.doit`. If ``noconds=True``, only `F` will be returned (i.e. not ``cond``, and also not the plane ``a``). .. deprecated:: 1.9 Legacy behavior for matrices where ``laplace_transform`` with ``noconds=False`` (the default) returns a Matrix whose elements are tuples. The behavior of ``laplace_transform`` for matrices will change in a future release of SymPy to return a tuple of the transformed Matrix and the convergence conditions for the matrix as a whole. Use ``legacy_matrix=False`` to enable the new behavior. Examples ======== >>> from sympy import DiracDelta, exp, laplace_transform >>> from sympy.abc import t, s, a >>> laplace_transform(t**4, t, s) (24/s**5, 0, True) >>> laplace_transform(t**a, t, s) (gamma(a + 1)/(s*s**a), 0, re(a) > -1) >>> laplace_transform(DiracDelta(t)-a*exp(-a*t), t, s, simplify=True) (s/(a + s), -re(a), True) There are also helper functions that make it easy to solve differential equations by Laplace transform. For example, to solve .. math :: m x''(t) + d x'(t) + k x(t) = 0 with initial value `0` and initial derivative `v`: >>> from sympy import Function, laplace_correspondence, diff, solve >>> from sympy import laplace_initial_conds, inverse_laplace_transform >>> from sympy.abc import d, k, m, v >>> x = Function('x') >>> X = Function('X') >>> f = m*diff(x(t), t, 2) + d*diff(x(t), t) + k*x(t) >>> F = laplace_transform(f, t, s, noconds=True) >>> F = laplace_correspondence(F, {x: X}) >>> F = laplace_initial_conds(F, t, {x: [0, v]}) >>> F d*s*X(s) + k*X(s) + m*(s**2*X(s) - v) >>> Xs = solve(F, X(s))[0] >>> Xs m*v/(d*s + k + m*s**2) >>> inverse_laplace_transform(Xs, s, t) 2*v*exp(-d*t/(2*m))*sin(t*sqrt((-d**2 + 4*k*m)/m**2)/2)*Heaviside(t)/sqrt((-d**2 + 4*k*m)/m**2) References ========== .. [1] Erdelyi, A. (ed.), Tables of Integral Transforms, Volume 1, Bateman Manuscript Prooject, McGraw-Hill (1954), available: https://resolver.caltech.edu/CaltechAUTHORS:20140123-101456353 See Also ======== inverse_laplace_transform, mellin_transform, fourier_transform hankel_transform, inverse_hankel_transform """ _noconds = hints.get('noconds', False) _simplify = hints.get('simplify', False) if isinstance(f, MatrixBase) and hasattr(f, 'applyfunc'): conds = not hints.get('noconds', False) if conds and legacy_matrix: adt = 'deprecated-laplace-transform-matrix' sympy_deprecation_warning( """ Calling laplace_transform() on a Matrix with noconds=False (the default) is deprecated. Either noconds=True or use legacy_matrix=False to get the new behavior. """, deprecated_since_version='1.9', active_deprecations_target=adt, ) # Temporarily disable the deprecation warning for non-Expr objects # in Matrix with ignore_warnings(SymPyDeprecationWarning): return f.applyfunc( lambda fij: laplace_transform(fij, t, s, **hints)) else: elements_trans = [laplace_transform( fij, t, s, **hints) for fij in f] if conds: elements, avals, conditions = zip(*elements_trans) f_laplace = type(f)(*f.shape, elements) return f_laplace, Max(*avals), And(*conditions) else: return type(f)(*f.shape, elements_trans) LT, p, c = LaplaceTransform(f, t, s).doit(noconds=False, simplify=_simplify) if not _noconds: return LT, p, c else: return LT @DEBUG_WRAP def _inverse_laplace_transform_integration(F, s, t_, plane, *, simplify): """ The backend function for inverse Laplace transforms. """ from sympy.integrals.meijerint import meijerint_inversion, _get_coeff_exp from sympy.integrals.transforms import inverse_mellin_transform # There are two strategies we can try: # 1) Use inverse mellin transform, related by a simple change of variables. # 2) Use the inversion integral. t = Dummy('t', real=True) def pw_simp(*args): """ Simplify a piecewise expression from hyperexpand. """ if len(args) != 3: return Piecewise(*args) arg = args[2].args[0].argument coeff, exponent = _get_coeff_exp(arg, t) e1 = args[0].args[0] e2 = args[1].args[0] return ( Heaviside(1/Abs(coeff) - t**exponent)*e1 + Heaviside(t**exponent - 1/Abs(coeff))*e2) if F.is_rational_function(s): F = F.apart(s) if F.is_Add: f = Add( *[_inverse_laplace_transform_integration(X, s, t, plane, simplify) for X in F.args]) return _simplify(f.subs(t, t_), simplify), True try: f, cond = inverse_mellin_transform(F, s, exp(-t), (None, S.Infinity), needeval=True, noconds=False) except IntegralTransformError: f = None if f is None: f = meijerint_inversion(F, s, t) if f is None: return None if f.is_Piecewise: f, cond = f.args[0] if f.has(Integral): return None else: cond = S.true f = f.replace(Piecewise, pw_simp) if f.is_Piecewise: # many of the functions called below can't work with piecewise # (b/c it has a bool in args) return f.subs(t, t_), cond u = Dummy('u') def simp_heaviside(arg, H0=S.Half): a = arg.subs(exp(-t), u) if a.has(t): return Heaviside(arg, H0) from sympy.solvers.inequalities import _solve_inequality rel = _solve_inequality(a > 0, u) if rel.lts == u: k = log(rel.gts) return Heaviside(t + k, H0) else: k = log(rel.lts) return Heaviside(-(t + k), H0) f = f.replace(Heaviside, simp_heaviside) def simp_exp(arg): return expand_complex(exp(arg)) f = f.replace(exp, simp_exp) return _simplify(f.subs(t, t_), simplify), cond @DEBUG_WRAP def _complete_the_square_in_denom(f, s): from sympy.simplify.radsimp import fraction [n, d] = fraction(f) if d.is_polynomial(s): cf = d.as_poly(s).all_coeffs() if len(cf) == 3: a, b, c = cf d = a*((s+b/(2*a))**2+c/a-(b/(2*a))**2) return n/d @cacheit def _inverse_laplace_build_rules(): """ This is an internal helper function that returns the table of inverse Laplace transform rules in terms of the time variable `t` and the frequency variable `s`. It is used by `_inverse_laplace_apply_rules`. """ s = Dummy('s') t = Dummy('t') a = Wild('a', exclude=[s]) b = Wild('b', exclude=[s]) c = Wild('c', exclude=[s]) _debug('_inverse_laplace_build_rules is building rules') def _frac(f, s): try: return f.factor(s) except PolynomialError: return f def same(f): return f # This list is sorted according to the prep function needed. _ILT_rules = [ (a/s, a, S.true, same, 1), ( b*(s+a)**(-c), t**(c-1)*exp(-a*t)/gamma(c), S.true, same, 1), (1/(s**2+a**2)**2, (sin(a*t) - a*t*cos(a*t))/(2*a**3), S.true, same, 1), # The next two rules must be there in that order. For the second # one, the condition would be a != 0 or, respectively, to take the # limit a -> 0 after the transform if a == 0. It is much simpler if # the case a == 0 has its own rule. (1/(s**b), t**(b - 1)/gamma(b), S.true, same, 1), (1/(s*(s+a)**b), lowergamma(b, a*t)/(a**b*gamma(b)), S.true, same, 1) ] return _ILT_rules, s, t @DEBUG_WRAP def _inverse_laplace_apply_simple_rules(f, s, t): """ Helper function for the class InverseLaplaceTransform. """ if f == 1: _debug(' rule: 1 o---o DiracDelta()') return DiracDelta(t), S.true _ILT_rules, s_, t_ = _inverse_laplace_build_rules() _prep = '' fsubs = f.subs({s: s_}) for s_dom, t_dom, check, prep, fac in _ILT_rules: if _prep != (prep, fac): _F = prep(fsubs*fac) _prep = (prep, fac) ma = _F.match(s_dom) if ma: c = check if c is not S.true: args = [x.xreplace(ma) for x in c[0]] c = c[1](*args) if c == S.true: return Heaviside(t)*t_dom.xreplace(ma).subs({t_: t}), S.true return None @DEBUG_WRAP def _inverse_laplace_diff(f, s, t, plane): """ Helper function for the class InverseLaplaceTransform. """ a = Wild('a', exclude=[s]) n = Wild('n', exclude=[s]) g = Wild('g') ma = f.match(a*Derivative(g, (s, n))) if ma and ma[n].is_integer: _debug(' rule: t**n*f(t) o---o (-1)**n*diff(F(s), s, n)') r, c = _inverse_laplace_transform( ma[g], s, t, plane, simplify=False, dorational=False) return (-t)**ma[n]*r, c return None @DEBUG_WRAP def _inverse_laplace_time_shift(F, s, t, plane): """ Helper function for the class InverseLaplaceTransform. """ a = Wild('a', exclude=[s]) g = Wild('g') if not F.has(s): return F*DiracDelta(t), S.true if not F.has(exp): return None ma1 = F.match(exp(a*s)) if ma1: if ma1[a].is_negative: _debug(' rule: exp(-a*s) o---o DiracDelta(t-a)') return DiracDelta(t+ma1[a]), S.true else: return InverseLaplaceTransform(F, s, t, plane), S.true ma1 = F.match(exp(a*s)*g) if ma1: if ma1[a].is_negative: _debug(' rule: exp(-a*s)*F(s) o---o Heaviside(t-a)*f(t-a)') return _inverse_laplace_transform( ma1[g], s, t+ma1[a], plane, simplify=False, dorational=True) else: return InverseLaplaceTransform(F, s, t, plane), S.true return None @DEBUG_WRAP def _inverse_laplace_freq_shift(F, s, t, plane): """ Helper function for the class InverseLaplaceTransform. """ if not F.has(s): return F*DiracDelta(t), S.true if len(args := F.args) == 1: a = Wild('a', exclude=[s]) if (ma := args[0].match(s-a)) and re(ma[a]).is_positive: _debug(' rule: F(s-a) o---o exp(-a*t)*f(t)') return ( exp(-ma[a]*t) * InverseLaplaceTransform(F.func(s), s, t, plane), S.true) return None @DEBUG_WRAP def _inverse_laplace_time_diff(F, s, t, plane): """ Helper function for the class InverseLaplaceTransform. """ n = Wild('n', exclude=[s]) g = Wild('g') ma1 = F.match(s**n*g) if ma1 and ma1[n].is_integer and ma1[n].is_positive: _debug(' rule: s**n*F(s) o---o diff(f(t), t, n)') r, c = _inverse_laplace_transform( ma1[g], s, t, plane, simplify=False, dorational=True) r = r.replace(Heaviside(t), 1) if r.has(InverseLaplaceTransform): return diff(r, t, ma1[n]), c else: return Heaviside(t)*diff(r, t, ma1[n]), c return None @DEBUG_WRAP def _inverse_laplace_irrational(fn, s, t, plane): """ Helper function for the class InverseLaplaceTransform. """ a = Wild('a', exclude=[s]) b = Wild('b', exclude=[s]) m = Wild('m', exclude=[s]) n = Wild('n', exclude=[s]) result = None condition = S.true fa = fn.as_ordered_factors() ma = [x.match((a*s**m+b)**n) for x in fa] if None in ma: return None constants = S.One zeros = [] poles = [] rest = [] for term in ma: if term[a] == 0: constants = constants*term elif term[n].is_positive: zeros.append(term) elif term[n].is_negative: poles.append(term) else: rest.append(term) # The code below assumes that the poles are sorted in a specific way: poles = sorted(poles, key=lambda x: (x[n], x[b] != 0, x[b])) zeros = sorted(zeros, key=lambda x: (x[n], x[b] != 0, x[b])) if len(rest) != 0: return None if len(poles) == 1 and len(zeros) == 0: if poles[0][n] == -1 and poles[0][m] == S.Half: # 1/(a0*sqrt(s)+b0) == 1/a0 * 1/(sqrt(s)+b0/a0) a_ = poles[0][b]/poles[0][a] k_ = 1/poles[0][a]*constants if a_.is_positive: result = ( k_/sqrt(pi)/sqrt(t) - k_*a_*exp(a_**2*t)*erfc(a_*sqrt(t))) _debug(' rule 5.3.4') elif poles[0][n] == -2 and poles[0][m] == S.Half: # 1/(a0*sqrt(s)+b0)**2 == 1/a0**2 * 1/(sqrt(s)+b0/a0)**2 a_sq = poles[0][b]/poles[0][a] a_ = a_sq**2 k_ = 1/poles[0][a]**2*constants if a_sq.is_positive: result = ( k_*(1 - 2/sqrt(pi)*sqrt(a_)*sqrt(t) + (1-2*a_*t)*exp(a_*t)*(erf(sqrt(a_)*sqrt(t))-1))) _debug(' rule 5.3.10') elif poles[0][n] == -3 and poles[0][m] == S.Half: # 1/(a0*sqrt(s)+b0)**3 == 1/a0**3 * 1/(sqrt(s)+b0/a0)**3 a_ = poles[0][b]/poles[0][a] k_ = 1/poles[0][a]**3*constants if a_.is_positive: result = ( k_*(2/sqrt(pi)*(a_**2*t+1)*sqrt(t) - a_*t*exp(a_**2*t)*(2*a_**2*t+3)*erfc(a_*sqrt(t)))) _debug(' rule 5.3.13') elif poles[0][n] == -4 and poles[0][m] == S.Half: # 1/(a0*sqrt(s)+b0)**4 == 1/a0**4 * 1/(sqrt(s)+b0/a0)**4 a_ = poles[0][b]/poles[0][a] k_ = 1/poles[0][a]**4*constants/3 if a_.is_positive: result = ( k_*(t*(4*a_**4*t**2+12*a_**2*t+3)*exp(a_**2*t) * erfc(a_*sqrt(t)) - 2/sqrt(pi)*a_**3*t**(S(5)/2)*(2*a_**2*t+5))) _debug(' rule 5.3.16') elif poles[0][n] == -S.Half and poles[0][m] == 2: # 1/sqrt(a0*s**2+b0) == 1/sqrt(a0) * 1/sqrt(s**2+b0/a0) a_ = sqrt(poles[0][b]/poles[0][a]) k_ = 1/sqrt(poles[0][a])*constants result = (k_*(besselj(0, a_*t))) _debug(' rule 5.3.35/44') elif len(poles) == 1 and len(zeros) == 1: if ( poles[0][n] == -3 and poles[0][m] == S.Half and zeros[0][n] == S.Half and zeros[0][b] == 0): # sqrt(az*s)/(ap*sqrt(s+bp)**3) # == sqrt(az)/ap * sqrt(s)/(sqrt(s+bp)**3) a_ = poles[0][b] k_ = sqrt(zeros[0][a])/poles[0][a]*constants result = ( k_*(2*a_**4*t**2+5*a_**2*t+1)*exp(a_**2*t) * erfc(a_*sqrt(t)) - 2/sqrt(pi)*a_*(a_**2*t+2)*sqrt(t)) _debug(' rule 5.3.14') if ( poles[0][n] == -1 and poles[0][m] == 1 and zeros[0][n] == S.Half and zeros[0][m] == 1): # sqrt(az*s+bz)/(ap*s+bp) # == sqrt(az)/ap * (sqrt(s+bz/az)/(s+bp/ap)) a_ = zeros[0][b]/zeros[0][a] b_ = poles[0][b]/poles[0][a] k_ = sqrt(zeros[0][a])/poles[0][a]*constants result = ( k_*(exp(-a_*t)/sqrt(t)/sqrt(pi)+sqrt(a_-b_) * exp(-b_*t)*erf(sqrt(a_-b_)*sqrt(t)))) _debug(' rule 5.3.22') elif len(poles) == 2 and len(zeros) == 0: if ( poles[0][n] == -1 and poles[0][m] == 1 and poles[1][n] == -S.Half and poles[1][m] == 1 and poles[1][b] == 0): # 1/((a0*s+b0)*sqrt(a1*s)) # == 1/(a0*sqrt(a1)) * 1/((s+b0/a0)*sqrt(s)) a_ = -poles[0][b]/poles[0][a] k_ = 1/sqrt(poles[1][a])/poles[0][a]*constants if a_.is_positive: result = (k_/sqrt(a_)*exp(a_*t)*erf(sqrt(a_)*sqrt(t))) _debug(' rule 5.3.1') elif ( poles[0][n] == -1 and poles[0][m] == 1 and poles[0][b] == 0 and poles[1][n] == -1 and poles[1][m] == S.Half): # 1/(a0*s*(a1*sqrt(s)+b1)) # == 1/(a0*a1) * 1/(s*(sqrt(s)+b1/a1)) a_ = poles[1][b]/poles[1][a] k_ = 1/poles[0][a]/poles[1][a]/a_*constants if a_.is_positive: result = k_*(1-exp(a_**2*t)*erfc(a_*sqrt(t))) _debug(' rule 5.3.5') elif ( poles[0][n] == -1 and poles[0][m] == S.Half and poles[1][n] == -S.Half and poles[1][m] == 1 and poles[1][b] == 0): # 1/((a0*sqrt(s)+b0)*(sqrt(a1*s)) # == 1/(a0*sqrt(a1)) * 1/((sqrt(s)+b0/a0)"sqrt(s)) a_ = poles[0][b]/poles[0][a] k_ = 1/(poles[0][a]*sqrt(poles[1][a]))*constants if a_.is_positive: result = k_*exp(a_**2*t)*erfc(a_*sqrt(t)) _debug(' rule 5.3.7') elif ( poles[0][n] == -S(3)/2 and poles[0][m] == 1 and poles[0][b] == 0 and poles[1][n] == -1 and poles[1][m] == S.Half): # 1/((a0**(3/2)*s**(3/2))*(a1*sqrt(s)+b1)) # == 1/(a0**(3/2)*a1) 1/((s**(3/2))*(sqrt(s)+b1/a1)) # Note that Bateman54 5.3 (8) is incorrect; there (sqrt(p)+a) # should be (sqrt(p)+a)**(-1). a_ = poles[1][b]/poles[1][a] k_ = 1/(poles[0][a]**(S(3)/2)*poles[1][a])/a_**2*constants if a_.is_positive: result = ( k_*(2/sqrt(pi)*a_*sqrt(t)+exp(a_**2*t)*erfc(a_*sqrt(t))-1)) _debug(' rule 5.3.8') elif ( poles[0][n] == -2 and poles[0][m] == S.Half and poles[1][n] == -1 and poles[1][m] == 1 and poles[1][b] == 0): # 1/((a0*sqrt(s)+b0)**2*a1*s) # == 1/a0**2/a1 * 1/(sqrt(s)+b0/a0)**2/s a_sq = poles[0][b]/poles[0][a] a_ = a_sq**2 k_ = 1/poles[0][a]**2/poles[1][a]*constants if a_sq.is_positive: result = ( k_*(1/a_ + (2*t-1/a_)*exp(a_*t)*erfc(sqrt(a_)*sqrt(t)) - 2/sqrt(pi)/sqrt(a_)*sqrt(t))) _debug(' rule 5.3.11') elif ( poles[0][n] == -2 and poles[0][m] == S.Half and poles[1][n] == -S.Half and poles[1][m] == 1 and poles[1][b] == 0): # 1/((a0*sqrt(s)+b0)**2*sqrt(a1*s)) # == 1/a0**2/sqrt(a1) * 1/(sqrt(s)+b0/a0)**2/sqrt(s) a_ = poles[0][b]/poles[0][a] k_ = 1/poles[0][a]**2/sqrt(poles[1][a])*constants if a_.is_positive: result = ( k_*(2/sqrt(pi)*sqrt(t) - 2*a_*t*exp(a_**2*t)*erfc(a_*sqrt(t)))) _debug(' rule 5.3.12') elif ( poles[0][n] == -3 and poles[0][m] == S.Half and poles[1][n] == -S.Half and poles[1][m] == 1 and poles[1][b] == 0): # 1 / (sqrt(a1*s)*(a0*sqrt(s+b0)**3)) # == 1/(sqrt(a1)*a0) * 1/(sqrt(s)*(sqrt(s+b0)**3)) a_ = poles[0][b] k_ = constants/sqrt(poles[1][a])/poles[0][a] result = k_*( (2*a_**2*t+1)*t*exp(a_**2*t)*erfc(a_*sqrt(t)) - 2/sqrt(pi)*a_*t**(S(3)/2)) _debug(' rule 5.3.15') elif ( poles[0][n] == -1 and poles[0][m] == 1 and poles[1][n] == -S.Half and poles[1][m] == 1): # 1 / ( (a0*s+b0)* sqrt(a1*s+b1) ) # == 1/(sqrt(a1)*a0) * 1 / ( (s+b0/a0)* sqrt(s+b1/a1) ) a_ = poles[0][b]/poles[0][a] b_ = poles[1][b]/poles[1][a] k_ = constants/sqrt(poles[1][a])/poles[0][a] result = k_*( 1/sqrt(b_-a_)*exp(-a_*t)*erf(sqrt(b_-a_)*sqrt(t))) _debug(' rule 5.3.23') elif len(poles) == 2 and len(zeros) == 1: if ( poles[0][n] == -1 and poles[0][m] == 1 and poles[1][n] == -1 and poles[1][m] == S.Half and zeros[0][n] == S.Half and zeros[0][m] == 1 and zeros[0][b] == 0): # sqrt(za0*s)/((a0*s+b0)*(a1*sqrt(s)+b1)) # == sqrt(za0)/(a0*a1) * s/((s+b0/a0)*(sqrt(s)+b1/a1)) a_sq = poles[1][b]/poles[1][a] a_ = a_sq**2 b_ = -poles[0][b]/poles[0][a] k_ = sqrt(zeros[0][a])/poles[0][a]/poles[1][a]/(a_-b_)*constants if a_sq.is_positive and b_.is_positive: result = k_*( a_*exp(a_*t)*erfc(sqrt(a_)*sqrt(t)) + sqrt(a_)*sqrt(b_)*exp(b_*t)*erfc(sqrt(b_)*sqrt(t)) - b_*exp(b_*t)) _debug(' rule 5.3.6') elif ( poles[0][n] == -1 and poles[0][m] == 1 and poles[0][b] == 0 and poles[1][n] == -1 and poles[1][m] == S.Half and zeros[0][n] == 1 and zeros[0][m] == S.Half): # (az*sqrt(s)+bz)/(a0*s*(a1*sqrt(s)+b1)) # == az/a0/a1 * (sqrt(z)+bz/az)/(s*(sqrt(s)+b1/a1)) a_num = zeros[0][b]/zeros[0][a] a_ = poles[1][b]/poles[1][a] if a_+a_num == 0: k_ = zeros[0][a]/poles[0][a]/poles[1][a]*constants result = k_*( 2*exp(a_**2*t)*erfc(a_*sqrt(t))-1) _debug(' rule 5.3.17') elif ( poles[1][n] == -1 and poles[1][m] == 1 and poles[1][b] == 0 and poles[0][n] == -2 and poles[0][m] == S.Half and zeros[0][n] == 2 and zeros[0][m] == S.Half): # (az*sqrt(s)+bz)**2/(a1*s*(a0*sqrt(s)+b0)**2) # == az**2/a1/a0**2 * (sqrt(z)+bz/az)**2/(s*(sqrt(s)+b0/a0)**2) a_num = zeros[0][b]/zeros[0][a] a_ = poles[0][b]/poles[0][a] if a_+a_num == 0: k_ = zeros[0][a]**2/poles[1][a]/poles[0][a]**2*constants result = k_*( 1 + 8*a_**2*t*exp(a_**2*t)*erfc(a_*sqrt(t)) - 8/sqrt(pi)*a_*sqrt(t)) _debug(' rule 5.3.18') elif ( poles[1][n] == -1 and poles[1][m] == 1 and poles[1][b] == 0 and poles[0][n] == -3 and poles[0][m] == S.Half and zeros[0][n] == 3 and zeros[0][m] == S.Half): # (az*sqrt(s)+bz)**3/(a1*s*(a0*sqrt(s)+b0)**3) # == az**3/a1/a0**3 * (sqrt(z)+bz/az)**3/(s*(sqrt(s)+b0/a0)**3) a_num = zeros[0][b]/zeros[0][a] a_ = poles[0][b]/poles[0][a] if a_+a_num == 0: k_ = zeros[0][a]**3/poles[1][a]/poles[0][a]**3*constants result = k_*( 2*(8*a_**4*t**2+8*a_**2*t+1)*exp(a_**2*t) * erfc(a_*sqrt(t))-8/sqrt(pi)*a_*sqrt(t)*(2*a_**2*t+1)-1) _debug(' rule 5.3.19') elif len(poles) == 3 and len(zeros) == 0: if ( poles[0][n] == -1 and poles[0][b] == 0 and poles[0][m] == 1 and poles[1][n] == -1 and poles[1][m] == 1 and poles[2][n] == -S.Half and poles[2][m] == 1): # 1/((a0*s)*(a1*s+b1)*sqrt(a2*s)) # == 1/(a0*a1*sqrt(a2)) * 1/((s)*(s+b1/a1)*sqrt(s)) a_ = -poles[1][b]/poles[1][a] k_ = 1/poles[0][a]/poles[1][a]/sqrt(poles[2][a])*constants if a_.is_positive: result = k_ * ( a_**(-S(3)/2) * exp(a_*t) * erf(sqrt(a_)*sqrt(t)) - 2/a_/sqrt(pi)*sqrt(t)) _debug(' rule 5.3.2') elif ( poles[0][n] == -1 and poles[0][m] == 1 and poles[1][n] == -1 and poles[1][m] == S.Half and poles[2][n] == -S.Half and poles[2][m] == 1 and poles[2][b] == 0): # 1/((a0*s+b0)*(a1*sqrt(s)+b1)*(sqrt(a2)*sqrt(s))) # == 1/(a0*a1*sqrt(a2)) * 1/((s+b0/a0)*(sqrt(s)+b1/a1)*sqrt(s)) a_sq = poles[1][b]/poles[1][a] a_ = a_sq**2 b_ = -poles[0][b]/poles[0][a] k_ = ( 1/poles[0][a]/poles[1][a]/sqrt(poles[2][a]) / (sqrt(b_)*(a_-b_))) if a_sq.is_positive and b_.is_positive: result = k_ * ( sqrt(b_)*exp(a_*t)*erfc(sqrt(a_)*sqrt(t)) + sqrt(a_)*exp(b_*t)*erf(sqrt(b_)*sqrt(t)) - sqrt(b_)*exp(b_*t)) _debug(' rule 5.3.9') if result is None: return None else: return Heaviside(t)*result, condition @DEBUG_WRAP def _inverse_laplace_early_prog_rules(F, s, t, plane): """ Helper function for the class InverseLaplaceTransform. """ prog_rules = [_inverse_laplace_irrational] for p_rule in prog_rules: if (r := p_rule(F, s, t, plane)) is not None: return r return None @DEBUG_WRAP def _inverse_laplace_apply_prog_rules(F, s, t, plane): """ Helper function for the class InverseLaplaceTransform. """ prog_rules = [_inverse_laplace_time_shift, _inverse_laplace_freq_shift, _inverse_laplace_time_diff, _inverse_laplace_diff, _inverse_laplace_irrational] for p_rule in prog_rules: if (r := p_rule(F, s, t, plane)) is not None: return r return None @DEBUG_WRAP def _inverse_laplace_expand(fn, s, t, plane): """ Helper function for the class InverseLaplaceTransform. """ if fn.is_Add: return None r = expand(fn, deep=False) if r.is_Add: return _inverse_laplace_transform( r, s, t, plane, simplify=False, dorational=True) r = expand_mul(fn) if r.is_Add: return _inverse_laplace_transform( r, s, t, plane, simplify=False, dorational=True) r = expand(fn) if r.is_Add: return _inverse_laplace_transform( r, s, t, plane, simplify=False, dorational=True) if fn.is_rational_function(s): r = fn.apart(s).doit() if r.is_Add: return _inverse_laplace_transform( r, s, t, plane, simplify=False, dorational=True) return None @DEBUG_WRAP def _inverse_laplace_rational(fn, s, t, plane, *, simplify): """ Helper function for the class InverseLaplaceTransform. """ x_ = symbols('x_') f = fn.apart(s) terms = Add.make_args(f) terms_t = [] conditions = [S.true] for term in terms: [n, d] = term.as_numer_denom() dc = d.as_poly(s).all_coeffs() dc_lead = dc[0] dc = [x/dc_lead for x in dc] nc = [x/dc_lead for x in n.as_poly(s).all_coeffs()] if len(dc) == 1: r = nc[0]*DiracDelta(t) terms_t.append(r) elif len(dc) == 2: r = nc[0]*exp(-dc[1]*t) terms_t.append(Heaviside(t)*r) elif len(dc) == 3: a = dc[1]/2 b = (dc[2]-a**2).factor() if len(nc) == 1: nc = [S.Zero] + nc l, m = tuple(nc) if b == 0: r = (m*t+l*(1-a*t))*exp(-a*t) else: hyp = False if b.is_negative: b = -b hyp = True b2 = list(roots(x_**2-b, x_).keys())[0] bs = sqrt(b).simplify() if hyp: r = ( l*exp(-a*t)*cosh(b2*t) + (m-a*l) / bs*exp(-a*t)*sinh(bs*t)) else: r = l*exp(-a*t)*cos(b2*t) + (m-a*l)/bs*exp(-a*t)*sin(bs*t) terms_t.append(Heaviside(t)*r) else: ft, cond = _inverse_laplace_transform( term, s, t, plane, simplify=simplify, dorational=False) terms_t.append(ft) conditions.append(cond) result = Add(*terms_t) if simplify: result = result.simplify(doit=False) return result, And(*conditions) @DEBUG_WRAP def _inverse_laplace_transform(fn, s_, t_, plane, *, simplify, dorational): """ Front-end function of the inverse Laplace transform. It tries to apply all known rules recursively. If everything else fails, it tries to integrate. """ terms = Add.make_args(fn) terms_t = [] conditions = [] for term in terms: if term.has(exp): # Simplify expressions with exp() such that time-shifted # expressions have negative exponents in the numerator instead of # positive exponents in the numerator and denominator; this is a # (necessary) trick. It will, for example, convert # (s**2*exp(2*s) + 4*exp(s) - 4)*exp(-2*s)/(s*(s**2 + 1)) into # (s**2 + 4*exp(-s) - 4*exp(-2*s))/(s*(s**2 + 1)) term = term.subs(s_, -s_).together().subs(s_, -s_) k, f = term.as_independent(s_, as_Add=False) if ( dorational and term.is_rational_function(s_) and (r := _inverse_laplace_rational( f, s_, t_, plane, simplify=simplify)) is not None or (r := _inverse_laplace_apply_simple_rules(f, s_, t_)) is not None or (r := _inverse_laplace_early_prog_rules(f, s_, t_, plane)) is not None or (r := _inverse_laplace_expand(f, s_, t_, plane)) is not None or (r := _inverse_laplace_apply_prog_rules(f, s_, t_, plane)) is not None): pass elif any(undef.has(s_) for undef in f.atoms(AppliedUndef)): # If there are undefined functions f(t) then integration is # unlikely to do anything useful so we skip it and given an # unevaluated LaplaceTransform. r = (InverseLaplaceTransform(f, s_, t_, plane), S.true) elif ( r := _inverse_laplace_transform_integration( f, s_, t_, plane, simplify=simplify)) is not None: pass else: r = (InverseLaplaceTransform(f, s_, t_, plane), S.true) (ri_, ci_) = r terms_t.append(k*ri_) conditions.append(ci_) result = Add(*terms_t) if simplify: result = result.simplify(doit=False) condition = And(*conditions) return result, condition class InverseLaplaceTransform(IntegralTransform): """ Class representing unevaluated inverse Laplace transforms. For usage of this class, see the :class:`IntegralTransform` docstring. For how to compute inverse Laplace transforms, see the :func:`inverse_laplace_transform` docstring. """ _name = 'Inverse Laplace' _none_sentinel = Dummy('None') _c = Dummy('c') def __new__(cls, F, s, x, plane, **opts): if plane is None: plane = InverseLaplaceTransform._none_sentinel return IntegralTransform.__new__(cls, F, s, x, plane, **opts) @property def fundamental_plane(self): plane = self.args[3] if plane is InverseLaplaceTransform._none_sentinel: plane = None return plane def _compute_transform(self, F, s, t, **hints): return _inverse_laplace_transform_integration( F, s, t, self.fundamental_plane, **hints) def _as_integral(self, F, s, t): c = self.__class__._c return ( Integral(exp(s*t)*F, (s, c - S.ImaginaryUnit*S.Infinity, c + S.ImaginaryUnit*S.Infinity)) / (2*S.Pi*S.ImaginaryUnit)) def doit(self, **hints): """ Try to evaluate the transform in closed form. Explanation =========== Standard hints are the following: - ``noconds``: if True, do not return convergence conditions. The default setting is `True`. - ``simplify``: if True, it simplifies the final result. The default setting is `False`. """ _noconds = hints.get('noconds', True) _simplify = hints.get('simplify', False) debugf('[ILT doit] (%s, %s, %s)', (self.function, self.function_variable, self.transform_variable)) s_ = self.function_variable t_ = self.transform_variable fn = self.function plane = self.fundamental_plane r = _inverse_laplace_transform( fn, s_, t_, plane, simplify=_simplify, dorational=True) if _noconds: return r[0] else: return r def inverse_laplace_transform(F, s, t, plane=None, **hints): r""" Compute the inverse Laplace transform of `F(s)`, defined as .. math :: f(t) = \frac{1}{2\pi i} \int_{c-i\infty}^{c+i\infty} e^{st} F(s) \mathrm{d}s, for `c` so large that `F(s)` has no singularites in the half-plane `\operatorname{Re}(s) > c-\epsilon`. Explanation =========== The plane can be specified by argument ``plane``, but will be inferred if passed as None. Under certain regularity conditions, this recovers `f(t)` from its Laplace Transform `F(s)`, for non-negative `t`, and vice versa. If the integral cannot be computed in closed form, this function returns an unevaluated :class:`InverseLaplaceTransform` object. Note that this function will always assume `t` to be real, regardless of the SymPy assumption on `t`. For a description of possible hints, refer to the docstring of :func:`sympy.integrals.transforms.IntegralTransform.doit`. Examples ======== >>> from sympy import inverse_laplace_transform, exp, Symbol >>> from sympy.abc import s, t >>> a = Symbol('a', positive=True) >>> inverse_laplace_transform(exp(-a*s)/s, s, t) Heaviside(-a + t) See Also ======== laplace_transform hankel_transform, inverse_hankel_transform """ _noconds = hints.get('noconds', True) _simplify = hints.get('simplify', False) if isinstance(F, MatrixBase) and hasattr(F, 'applyfunc'): return F.applyfunc( lambda Fij: inverse_laplace_transform(Fij, s, t, plane, **hints)) r, c = InverseLaplaceTransform(F, s, t, plane).doit( noconds=False, simplify=_simplify) if _noconds: return r else: return r, c def _fast_inverse_laplace(e, s, t): """Fast inverse Laplace transform of rational function including RootSum""" a, b, n = symbols('a, b, n', cls=Wild, exclude=[s]) def _ilt(e): if not e.has(s): return e elif e.is_Add: return _ilt_add(e) elif e.is_Mul: return _ilt_mul(e) elif e.is_Pow: return _ilt_pow(e) elif isinstance(e, RootSum): return _ilt_rootsum(e) else: raise NotImplementedError def _ilt_add(e): return e.func(*map(_ilt, e.args)) def _ilt_mul(e): coeff, expr = e.as_independent(s) if expr.is_Mul: raise NotImplementedError return coeff * _ilt(expr) def _ilt_pow(e): match = e.match((a*s + b)**n) if match is not None: nm, am, bm = match[n], match[a], match[b] if nm.is_Integer and nm < 0: return t**(-nm-1)*exp(-(bm/am)*t)/(am**-nm*gamma(-nm)) if nm == 1: return exp(-(bm/am)*t) / am raise NotImplementedError def _ilt_rootsum(e): expr = e.fun.expr [variable] = e.fun.variables return RootSum(e.poly, Lambda(variable, together(_ilt(expr)))) return _ilt(e)