#2452: [with patch, needs work] Heaviside step function, Dirac delta needed
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Reporter: gfurnish | Owner: gfurnish
Type: enhancement | Status: assigned
Priority: major | Milestone: sage-4.1
Component: symbolics | Keywords:
Reviewer: | Author:
Merged: |
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Changes (by burcin):
* priority: critical => major
Comment:
Replying to [comment:11 gmhossain]:
> > The testing didn't reveal any failures related to the patch. However,
I'm also wondering about
> > this output:
{{{
sage: f(x) = heaviside(x)+dirac_delta(x)
sage: f(1)
dirac_delta(1) + heaviside(1)
}}}
>
> It seems, you have hit a bug in new symbolics. The similar non-
evaluation
> of symbolic function is happening even with other functions such as sin,
cos.
> I posted this issue here
>
> http://groups.google.com/group/sage-
devel/browse_thread/thread/3936d1290ee933a6
>
> Burcin wrote that this is a bug and it is to be fixed in the new version
of pynac.
This is a different issue than the one you posted on sage-devel.
In your patch, you are not telling pynac how to evaluate the function you
define. This is done by defining an `_eval_` method, so if you move the
contents of your `__call__` function to `_eval_` and remove the last
`SFunction.__call__` line things should work fine. I agree that this is
confusing. It's one of the main points I wanted to address while
refactoring symbolic functions.
I would also like to see a `.sub()` test added, since this is the easiest
way to test if the `_eval_` function is defined properly. E.g.,
{{{
sage: dirac_delta(x).sub(x=1)
0
sage: heaviside(x).sub(x=1)
1
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/2452#comment:12>
Sage <http://sagemath.org/>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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