[with patch, positive review] invalid array elements sent to matplotlib quiver, causing blank plot

[jason]

A student noticed that sometimes, when a function evaluation gave Inf or NaN, the vector field plot was blank. Discussing this on the matplotlib-users list revealed that we ought to mask our arrays before sending them to the matplotlib quiver function. This patch corrects this, so that the plot:

plot_vector_field( (-x/sqrt(x^2+y^2), -y/sqrt(x^2+y^2)), (x, -10, 10), (y, -10, 10))

now plots (before it was a blank plot, now it just skips the problematic vectors).

[jason]

To test this, you might try the following plots before and after the patch:

        sage: var('x,y')
        sage: plot_vector_field( (-x/sqrt(x^2+y^2), -y/sqrt(x^2+y^2)), (x, -10, 10), (y, -10, 10))
        sage: plot_vector_field( (-x/sqrt(x+y), -y/sqrt(x+y)), (x, -10, 10), (y, -10, 10))

[jason]

For the matplotlib-users discussion, see the messages with subject "quiver and Inf values" here:  http://sourceforge.net/mailarchive/forum.php?forum_name=matplotlib-users&max_rows=25&style=ultimate&viewmonth=200902&viewday=13

[jason]

updated patch corrects the silly mistake in the doctest (I didn't account for the output of var('x,y')). Now doctests pass in plot/*.py.

[hivert]

Everything look good !

[jason]

Robert Nelson should be listed as the reporter of this bug.

[mabshoff]

Merged in Sage 3.3.rc1.

Cheers,

Michael