You should file a ticket. Symbols are getting mixed up. Recently there were
some changes to the order in which different integration algorithms are
used, and I suspect that this happens as a side effect.
I can tell you what I see happen:
This is what the actual "unit_step" function should be.
sage: type(unit_step)
<class 'sage.functions.generalized.FunctionUnitStep'>
When you run into the error:
RuntimeError: Encountered operator mismatch in sr-to-maxima translation
we have a function "op" with the following properties:
ipdb> p op
unit_step
ipdb> p type(op)
<class 'sage.symbolic.function_factory.NewSymbolicFunction'>
so that's a function with the same print-name as "unit_step", but it's a
different function. The sage-to-maxima (and vice versa) dictionaries know
how to translate the original `unit_step`, but at this point it is noticed
that this "new" function `unit_step` would cause a name clash at the maxima
side. Hence the error. It seems to me the maxima interface is operating as
it should. The error is probably that the expression was manipulated (by
integrate) before that point by some interface; problably the sympy one;
which confused the system.
Smoking gun:
sage: type(unit_step(x).operator())
<class 'sage.functions.generalized.FunctionUnitStep'>
sage: type(unit_step(x)._sympy_()._sage_().operator())
<class 'sage.symbolic.function_factory.NewSymbolicFunction'>
Even if this is not the source of the bug you're experiencing this is
something that needs to be fixed: sympy needs to be taught about unit_step.
On Sunday, January 19, 2020 at 6:46:50 AM UTC-8, mendes wrote:
> Thank you Bruin and Kcrisman, for your attention.
>
> The following codes are examples of the problem:
>
> # fg denotes the convolution product f*g. The expected result is f*g = 0,
> if t < 1 and f*g = t^2/2-t+1/2, if t > 1.
> # For 0 < t < 1, it runs ok:
> var('x,t')
> assume(0<t,t<1)
> f=unit_step(t-1)
> g=t
> fg = integrate(f(t=x)*g(t=t-x),x,0,t).simplify_full().expand()
> show(fg)
> forget()
>
> #But, for t>1, there is a RuntimeError: mismatch in sr-to-maxima
> var('x,t')
> assume(1<t)
> f=unit_step(t-1)
> g=t
> fg = integrate(f(t=x)*g(t=t-x),x,0,t).simplify_full().expand()
> show(fg)
> forget()
>
> #In previous versions of Sage the answer, in the case piecewise functions
> like f*g, could employ the functions like sign() or abs(), but no
> Error messages appeared
>
> #The following alternative raises no Error, but does not evaluate the f*g
> function to t^2/2-t+1/2, as desired:
> var('x,t')
> assume(1<t)
> f=unit_step(t-1)
> g=t
> fg = integrate(f(t=x)*g(t=t-x),x,0,t,hold=False)
> show(fg)
> forget()
>
> Thank you again.
>
>
>
>>>
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