#15021: Return unevaluated derivative
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Reporter: eviatarbach | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-5.12
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Dependencies:
Stopgaps: |
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Description changed by eviatarbach:
Old description:
> There should be a way to return an unevaluated derivative from within the
> `_derivative_` or `_tderivative_` method of a `BuiltinFunction`. Perhaps
> by returning `None`, like `_eval_` does for remaining unevaluated. As of
> now returning `None` causes a segmentation fault.
>
> This is important because for multivariate functions often only the
> derivative with respect to one variable may be known, so we want to
> return the unevaluated derivative if it's taken with respect to a
> variable in which we don't know the derivative. Right now it seems the
> only way to not return a derivative is to raise an exception.
New description:
There should be a way to return an unevaluated derivative from within the
`_derivative_` or `_tderivative_` method of a `BuiltinFunction`. Perhaps
by returning `None`, like `_eval_` does for remaining unevaluated. As of
now returning `None` causes a segmentation fault.
This is important because for multivariate functions often only the
derivative with respect to one variable may be known, so we want to return
the unevaluated derivative if it's taken with respect to a variable in
which we don't know the derivative. Right now it seems the only way to not
return an evaluated derivative is to raise an exception.
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Ticket URL: <http://trac.sagemath.org/ticket/15021#comment:1>
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