This ask.sagemath question
<https://ask.sagemath.org/question/46819/numerical-integration-and-plot-failing/>
seems
to raise a genuine bug. Perusing Trac doesn't raise muc relevant, possibly
except for Trac#24428 <https://trac.sagemath.org/ticket/24428> and
Trac#21754 <https://trac.sagemath.org/ticket/21754>.
>From my comment to the ask.sagemath question :
Indeed :
sage: var("y,z")
(y, z)
sage: cauchy(z)=solve(z*y^3 +y^2 - 2*z*y+2 ,y)[0].rhs()
sage: def foo(u):return(arg(cauchy(u)).n())
sage: [foo(t) for t in (1,1.1..2)]
[0.828222717321238,
## Snip...
0.377665318352514]
Therefore, this function *can* be evaluated. But :
sage: plot(foo,(1,2))
verbose 0 (3635: plot.py, generate_plot_points) WARNING: When plotting,
failed to evaluate function at 200 points.
verbose 0 (3635: plot.py, generate_plot_points) Last error message:
'negative number cannot be raised to a fractional power'
Launched png viewer for Graphics object consisting of 0 graphics
primitives
... not in `plot`. Trying to plot symbolically yelds :
TypeError: Cannot evaluate symbolic expression to a numeric value.
A bug, IMHO.
Can someone confirm this and, possibly, give me hints as how to flag this
ticket efficiently ?
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