id summary reporter owner description type status priority milestone component resolution keywords cc merged author reviewer upstream work_issues branch commit dependencies stopgaps
13355 doctest proper handling of domain in evalf functions tkluck burcin "Previous description of ticket:
------------------------------------
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 to `float`, 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." defect closed major sage-6.3 symbolics fixed evalf, fast_callable kcrisman eviatarbach Timo Kluck Ralf Stephan N/A 65675e8384d489cd8c906cfa56be0c356334320f 65675e8384d489cd8c906cfa56be0c356334320f