Re: [matplotlib-devel] bug in vector plotting

[Eric F. <ef...@ha...>]

On 2012/08/29 10:07 AM, David Raymond wrote:
>
> I think that I have found a serious bug in vector plotting (quiver)
> when the "angle=xy" option is used on a plot with a large aspect
> ratio.  It is my understanding that with this option, the vector with
> tail at (x,y) would have its head at (x + vx,y + vy); at least this is
> what it says in the documentation.

Not a bug.
Note this in the documentation:

   *scale_units*: *None*, or any of the *units* options.
     For example, if *scale_units* is 'inches', *scale* is 2.0, and
     ``(u,v) = (1,0)``, then the vector will be 0.5 inches long.
     If *scale_units* is 'width', then the vector will be half the width
     of the axes.

     If *scale_units* is 'x' then the vector will be 0.5 x-axis
     units.  To plot vectors in the x-y plane, with u and v having
     the same units as x and y, use
     "angles='xy', scale_units='xy', scale=1".

Try this modified call to quiver:

q = plt.quiver(X, Y, vx, vy, angles='xy', scale_units='xy')

Eric