#13559: loglog plots of "large" function fail to find good evaluation points
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Reporter: nthiery | Owner: jason, was
Type: defect | Status: new
Priority: major | Milestone: sage-5.5
Component: graphics | Keywords:
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
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It sounds like the adaptative algorithm fails to find suitable
evaluation points when plotting large functions (like exp) in loglog
scale. In the following example, the exp function gets drawn with only
three points:
{{{
sage: plot([n^2,exp(n)], xmin=1, xmax=10^5, ymin=1,ymax=10^10,
scale="loglog")
verbose 0 (2397: plot.py, generate_plot_points) WARNING: When plotting,
failed to evaluate function at 198 points.
verbose 0 (2397: plot.py, generate_plot_points) Last error message: ''
}}}
If xmax is replaced by 10^10, the function is not even drawn:
{{{
sage: sage: plot([n^2,exp(n)], xmin=1, xmax=10^10, ymin=1,ymax=10^10,
scale="loglog")
verbose 0 (2397: plot.py, generate_plot_points) WARNING: When plotting,
failed to evaluate function at 199 points.
verbose 0 (2397: plot.py, generate_plot_points) Last error message: ''
}}}
On the other hand, the equivalent semilogy plot works smoothly:
{{{
sage: plot([10^n,exp(10^n)], xmin=0, xmax=5, ymin=1,ymax=10^10,
scale="semilogy")
verbose 0 (2397: plot.py, generate_plot_points) WARNING: When plotting,
failed to evaluate function at 86 points.
verbose 0 (2397: plot.py, generate_plot_points) Last error message: ''
}}}
(Such plots are typically useful in classes about algorithmic complexity
http://combinat.sagemath.org/doc/thematic_tutorials/agregation-option-
calcul-formel/tris_et_complexite.html)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13559>
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