Opened 8 years ago
Last modified 7 years ago
#13355 closed defect
Plot fails if a function implicitly needs complex intermediate values — at Version 2
Reported by: | tkluck | Owned by: | burcin |
---|---|---|---|
Priority: | major | Milestone: | sage-6.3 |
Component: | symbolics | Keywords: | evalf, fast_callable |
Cc: | kcrisman, eviatarbach | Merged in: | |
Authors: | Reviewers: | ||
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description (last modified by )
Plotting currently fails when plotting a symbolic function that evaluates to complex values:
sage: def evalf_func(self,x,parent=None): ....: return parent(I*x) if parent!=None else I*x ....: sage: f = function('f', evalf_func=evalf_func) sage: plot(abs(f(x)),0,5) verbose 0 (2392: plot.py, generate_plot_points) WARNING: When plotting, failed to evaluate function at 199 points. verbose 0 (2392: plot.py, generate_plot_points) Last error message: 'unable to simplify to float approximation'
This is because plot
uses fast_float
, and fast_float
cannot deal with the intermediate complex value.
The attached patch first changes these things:
- it adds a method to
class Function
that allows one to see what output range is to be expected for a given input range. By default, it will return a complex field. - it overrides this method for builtin functions, which return floats for float input
- this is then used by
fast_float
to throw an exception if complex values are to be expected
This exception will cause plot
to fall back to fast_callable
instead of fast_float
. However, fast_callable
needs patching too:
- it now uses the
_evalf_
method when available instead of just__call__
. Otherwise,plot
will try to coerce the result tofloat
, which also cannot deal with complex intermediate values.
An alternative to this step would be to fix float
coercion, which I haven't looked into.
Change History (3)
Changed 8 years ago by
comment:1 Changed 8 years ago by
- Status changed from new to needs_review
comment:2 Changed 8 years ago by
- Description modified (diff)
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