laplace_transform(cosh(2*x), x, s) raises RecursionError

[MaqOwais]

>>> from sympy import *
>>> from sympy.abc import x,y,z,s
>>> laplace_transform(cosh(x), x, s)
(s/(s**2 - 1), 1, True)

>>> laplace_transform(cosh(2*x), x, s)
RecursionError: maximum recursion depth exceeded while calling a Python object

[jksuom]

This piece of code looks incorrect:

sympy/sympy/functions/elementary/piecewise.py

Lines 179 to 183 in f9badb2

	if len(funcs) == 1 and len(
	c.xreplace({list(funcs)[0]: Dummy()}
	).free_symbols) == 1:
	# we can treat function like a symbol
	free = funcs

It should be removed.

[hanspi42]

Interestingly,

laplace_transform(cosh(2.0*x), x, s)

works.

[hanspi42]

Laplace transform of cosh is now implemented properly in #22376. Comments welcome.

[hanspi42]

@jksuom: #22376 was merged. This issue is resolved and can be closed.

[oscarbenjamin]

Since #22376 was merged this issue is no longer seen when calling laplace_transform. The underlying bug with simplify is still seen though:

In [5]: expr = parse_expr(
   ...:     "Piecewise((s*exp_polar(I*pi)/(4*(1 - s**2/4)), Abs(s**2)/4 < 1), (1/(s*(1 - 4/s**2)), 4/
   ...: Abs(s**2) < 1), (pi*meijerg(((1/2,), (0, 0)), ((0, 1/2), (0,)), s**2/4)/2, True))"
   ...: )

In [6]: expr
Out[6]: 
⎧              ⅈ⋅π                  │ 2│    
⎪           s⋅ℯ                     │s │    
⎪           ──────              for ──── < 1
⎪                2                   4      
⎪           4 - s                           
⎪                                           
⎪             1                      4      
⎪         ──────────            for ──── < 1
⎪           ⎛    4 ⎞                │ 2│    
⎨         s⋅⎜1 - ──⎟                │s │    
⎪           ⎜     2⎟                        
⎪           ⎝    s ⎠                        
⎪                                           
⎪          ⎛             │  2⎞              
⎪  ╭─╮2, 1 ⎜ 1/2    0, 0 │ s ⎟              
⎪π⋅│╶┐     ⎜             │ ──⎟              
⎪  ╰─╯3, 3 ⎝0, 1/2   0   │ 4 ⎠              
⎪─────────────────────────────   otherwise  
⎩              2                            

In [7]: simplify(expr)
...
RecursionError: maximum recursion depth exceeded while calling a Python object

The infinite recursion seems to be here:

sympy/sympy/functions/elementary/piecewise.py

Lines 290 to 291 in b9b33b4

	if missing or not same:
	return cls(*newargs)

[hanspi42]

Maybe this should get a different label for people working in simplify to find it. It can also lose the integrals.transforms label since that part is solved.