The issue boils down to this:
sage: var('t');function('u');
sage: laplace(u(t),t,t)
laplace(u(t), t, t)
sage: laplace(u(t),t,t+3)
ValueError: The name "+" is not a valid Python identifier.
The error is raised in dummy_laplace called with arguments (u(t),t,t+3),
when executing
var(repr(args[2])). That just looks like a very bad idea (the input IS
already a symbolic expression!), so very likely the implementation of
dummy_laplace needs some care.
As a sanity check:
sage: L=laplace(u(t),t,t).operator()
sage: L(u(t),t,t+3)
laplace(u(t), t, t + 3)
so there doesn't seem to be a problem with representing the particular
expression that maxima is returning.
On Tuesday, March 27, 2018 at 2:34:37 PM UTC-7, Dmytro Yeroshkin wrote:
>
> Running the following code:
>
> var('t')
> function('u')(t)
> function('v')(t)
> desolve_system([2*u(t)*sin(t) + diff(u(t),t) == 0, -cos(t)*u(t) +
> v(t)*sin(t) + diff(v(t),t) == 0], [u(t), v(t)], [0,1,0], t)
>
> results in an error message:
>
> ValueError: The name "+" is not a valid Python identifier.
>
> I have tested this on:
>
> Xubuntu 17.10 x64 Sage 8.0 shell compiled from source
> Windows 7 x64 Sage 8.0 and 8.1 notebooks from the sage-windows release
>
> I can post the full traceback of the error if needed, but I'm getting the
> same issue on 2 different computers.
>
> Dmytro
>
>
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