Here is the error
>>> inverse_laplace_transform(0.5/(.5*s+1)*1/s, s, t)
Traceback (most recent call last):
File "./sympy/polys/polyutils.py", line 211, in
_parallel_dict_from_expr_if_gens
monom[indices[base]] = exp
KeyError: RisingFactorial(_t + 1, 2.0)
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "./sympy/polys/partfrac.py", line 82, in apart
(P, Q), opt = parallel_poly_from_expr((P, Q), x, **options)
File "./sympy/polys/polytools.py", line 4301, in parallel_poly_from_expr
return _parallel_poly_from_expr(exprs, opt)
File "./sympy/polys/polytools.py", line 4354, in _parallel_poly_from_expr
reps, opt = _parallel_dict_from_expr(exprs, opt)
File "./sympy/polys/polyutils.py", line 332, in _parallel_dict_from_expr
reps, gens = _parallel_dict_from_expr_if_gens(exprs, opt)
File "./sympy/polys/polyutils.py", line 217, in
_parallel_dict_from_expr_if_gens
"the set of generators." % factor)
sympy.polys.polyerrors.PolynomialError: RisingFactorial(_t + 1, 2.0)
contains an element of the set of generators.
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "./sympy/integrals/transforms.py", line 1293, in
inverse_laplace_transform
return InverseLaplaceTransform(F, s, t, plane).doit(**hints)
File "./sympy/integrals/transforms.py", line 121, in doit
self.function_variable, self.transform_variable, **hints)
File "./sympy/integrals/transforms.py", line 1245, in _compute_transform
return _inverse_laplace_transform(F, s, t, self.fundamental_plane, **hints)
File "./sympy/integrals/transforms.py", line 206, in wrapper
res = func(*args, **kwargs)
File "./sympy/integrals/transforms.py", line 1172, in
_inverse_laplace_transform
needeval=True, noconds=False)
File "./sympy/integrals/transforms.py", line 875, in inverse_mellin_transform
return InverseMellinTransform(F, s, x, strip[0], strip[1]).doit(**hints)
File "./sympy/integrals/transforms.py", line 121, in doit
self.function_variable, self.transform_variable, **hints)
File "./sympy/integrals/transforms.py", line 819, in _compute_transform
return _inverse_mellin_transform(F, s, x, strip, **hints)
File "./sympy/integrals/transforms.py", line 206, in wrapper
res = func(*args, **kwargs)
File "./sympy/integrals/transforms.py", line 746, in _inverse_mellin_transform
h = hyperexpand(G)
File "./sympy/simplify/hyperexpand.py", line 2491, in hyperexpand
return f.replace(hyper, do_replace).replace(meijerg, do_meijer)
File "./sympy/core/basic.py", line 1508, in replace
rv = bottom_up(self, rec_replace, atoms=True)
File "./sympy/simplify/simplify.py", line 1152, in bottom_up
rv = F(rv)
File "./sympy/core/basic.py", line 1489, in rec_replace
new = _value(expr, result)
File "./sympy/core/basic.py", line 1437, in <lambda>
_value = lambda expr, result: value(*expr.args)
File "./sympy/simplify/hyperexpand.py", line 2488, in do_meijer
allow_hyper, rewrite=rewrite, place=place)
File "./sympy/simplify/hyperexpand.py", line 2373, in _meijergexpand
t, 1/z0)
File "./sympy/simplify/hyperexpand.py", line 2346, in do_slater
t, premult, au, rewrite=None)
File "./sympy/simplify/hyperexpand.py", line 2042, in _hyperexpand
formula = try_lerchphi(func)
File "./sympy/simplify/hyperexpand.py", line 1783, in try_lerchphi
part = apart(numer/denom, t)
File "./sympy/utilities/decorator.py", line 36, in threaded_func
return func(expr, *args, **kwargs)
File "./sympy/polys/partfrac.py", line 85, in apart
raise PolynomialError(msg)
sympy.polys.polyerrors.PolynomialError: RisingFactorial(_t + 1, 2.0)
contains an element of the set of generators.
It looks like somewhere in the integration algorithm it creates
RisingFactorial(t + 1, 2.0) expecting it to be converted to a
polynomial. But this only works if the second argument is an integer,
not a float
>>> RisingFactorial(t + 1, 2)
(t + 1)*(t + 2)
>>> RisingFactorial(t + 1, 2.0)
RisingFactorial(t + 1, 2.0)
I would suggest opening an issue for this.
Aaron Meurer
On Wed, May 6, 2020 at 3:00 PM Oscar Benjamin
<[email protected]> wrote:
>
> Hi Javier,
>
> I'm not sure exactly the problem with the example you showed. I think
> it's a bug somewhere.
>
> It is usually better not to use floats in sympy. With exact rational
> numbers your example works for me:
>
> In [17]: inverse_laplace_transform(S.Half/(S.Half*s+1)*1/s, s, t)
> Out[17]:
> -2⋅t
> θ(t) ℯ ⋅θ(t)
> ──── - ─────────
> 2 2
>
>
> Oscar
>
> On Wed, 6 May 2020 at 18:36, Javier Arantegui
> <[email protected]> wrote:
> >
> > Hello!
> >
> > I'm using Sympy 1.5.1 and Python is 3.7.7. Both installed using Anaconda.
> >
> > I have tried to do an inverse Laplace transform and I got an error:
> >
> > inverse_laplace_transform(0.5/(.5*s+1)*1/s, s, t)
> >
> > The error message is quite long, tell me if you need it.
> >
> > I spent 10 minutes in front of my students trying to think what was wrong...
> >
> > Finally, I was able to solve it with an easy change:
> >
> > inverse_laplace_transform(0.5*2/(2*(.5*s+1))*1/s, s, t)
> >
> >
> > Best regards,
> >
> > Javier
> >
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