#16587: f(expr,hold).n() fails for all generalized functions
-------------------------------------+-------------------------------------
Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: symbolics | Resolution:
Keywords: sgn, evaluation | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/rws/f_expr__n___fails_for_all_generalized_functions|
cc22a9b489a841b23a6e9455bfea80a0b423c0e1
Dependencies: #17130, #17285 | Stopgaps:
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Description changed by rws:
Old description:
> As reported in http://ask.sagemath.org/question/8535/problem-with-sign-
> sgn-and-n/ by Louis Cypher:
> {{{
> sage: M = sgn(cos(3/2))
> sage: M.n()
> TypeError Traceback (most recent call
> last)
> <ipython-input-5-0f11e9bd1e87> in <module>()
> ----> 1 M.n()
>
> /home/ralf/sage/local/lib/python2.7/site-
> packages/sage/symbolic/expression.so in
> sage.symbolic.expression.Expression._numerical_approx
> (build/cythonized/sage/symbolic/expression.cpp:24086)()
>
> TypeError: cannot evaluate symbolic expression numerically
> }}}
> kcrisman:
>
> Problem seems to be that in `M.n??` we see that it's looking for
> `is_a_numeric(x._gobj)` but apparently that fails, as does the constant,
> so it thinks we are looking at evaluating `sgn(cos(x))` instead of
> `sgn(cos(3/2))`.
>
> UPDATE:
> The problem also appears with `polylog(2.,.9).n()` for example.
New description:
{{{
sage: M = sgn((3/2),hold=True); M.n()
...
TypeError: cannot evaluate symbolic expression numerically
sage: polylog(2.,.9).n()
...
TypeError: cannot evaluate symbolic expression numerically
}}}
The original problem is now resolved, it was reported in
http://ask.sagemath.org/question/8535/problem-with-sign-sgn-and-n/ by
Louis Cypher:
{{{
sage: M = sgn(cos(3/2))
sage: M.n()
TypeError Traceback (most recent call
last)
<ipython-input-5-0f11e9bd1e87> in <module>()
----> 1 M.n()
/home/ralf/sage/local/lib/python2.7/site-
packages/sage/symbolic/expression.so in
sage.symbolic.expression.Expression._numerical_approx
(build/cythonized/sage/symbolic/expression.cpp:24086)()
TypeError: cannot evaluate symbolic expression numerically
}}}
kcrisman:
Problem seems to be that in `M.n??` we see that it's looking for
`is_a_numeric(x._gobj)` but apparently that fails, as does the constant,
so it thinks we are looking at evaluating `sgn(cos(x))` instead of
`sgn(cos(3/2))`.
--
--
Ticket URL: <http://trac.sagemath.org/ticket/16587#comment:20>
Sage <http://www.sagemath.org>
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