Re: [Matplotlib-users] quiver aspect ratio

[<jas...@cr...>]

Eric Firing wrote:
>>> Well, the easiest way is to build mpl from svn; a few minutes ago I 
>>> added this capability to quiver, selectable with an "angles" kwarg.

Eric,

I tried just copying the quiver.py SVN version 6114 into my existing 
matplotlib install and numpy 1.1.1.  When running my example posted 
earlier with the angles='xy' keyword added to the quiver call, I get the 
following error:

In [10]: show()
---------------------------------------------------------------------------
<type 'exceptions.ValueError'>            Traceback (most recent call last)

/usr/lib/python2.5/site-packages/matplotlib/backends/backend_gtk.py in 
expose_event(self, widget, event)
    331                 x, y, w, h = self.allocation
    332                 self._pixmap_prepare (w, h)
--> 333                 self._render_figure(self._pixmap, w, h)
    334                 self._need_redraw = False
    335

/usr/lib/python2.5/site-packages/matplotlib/backends/backend_gtkagg.py 
in _render_figure(self, pixmap, width, height)
     73     def _render_figure(self, pixmap, width, height):
     74         if DEBUG: print 'FigureCanvasGTKAgg.render_figure'
---> 75         FigureCanvasAgg.draw(self)
     76         if DEBUG: print 'FigureCanvasGTKAgg.render_figure 
pixmap', pixmap
     77         #agg_to_gtk_drawable(pixmap, self.renderer._renderer, None)

/usr/lib/python2.5/site-packages/matplotlib/backends/backend_agg.py in 
draw(self)
    259
    260         self.renderer = self.get_renderer()
--> 261         self.figure.draw(self.renderer)
    262
    263     def get_renderer(self):

/usr/lib/python2.5/site-packages/matplotlib/figure.py in draw(self, 
renderer)
    757
    758         # render the axes
--> 759         for a in self.axes: a.draw(renderer)
    760
    761         # render the figure text

/usr/lib/python2.5/site-packages/matplotlib/axes.py in draw(self, 
renderer, inframe)
   1521
   1522         for zorder, i, a in dsu:
-> 1523             a.draw(renderer)
   1524
   1525         renderer.close_group('axes')

/usr/lib/python2.5/site-packages/matplotlib/quiver.py in draw(self, 
renderer)
    423         self._init()
    424         if self._new_UV or self.angles == 'xy':
--> 425             verts = self._make_verts(self.U, self.V)
    426             self.set_verts(verts, closed=False)
    427             self._new_UV = False

/usr/lib/python2.5/site-packages/matplotlib/quiver.py in 
_make_verts(self, U, V)
    483         else:
    484             theta = ma.asarray(self.angles*np.pi/180.0).filled(0)
--> 485         xy = (X+Y*1j) * np.exp(1j*theta)*self.width
    486         xy = xy[:,:,np.newaxis]
    487         XY = ma.concatenate((xy.real, xy.imag), axis=2)

/usr/lib/python2.5/site-packages/numpy/ma/core.py in __mul__(self, other)
   1710     def __mul__(self, other):
   1711         "Multiply other by self, and return a new masked array."
-> 1712         return multiply(self, other)
   1713     #
   1714     def __div__(self, other):

/usr/lib/python2.5/site-packages/numpy/ma/core.py in __call__(self, a, 
b, *args, **kwargs)
    513         m = mask_or(getmask(a), getmask(b))
    514         (d1, d2) = (get_data(a), get_data(b))
--> 515         result = self.f(d1, d2, *args, 
**kwargs).view(get_masked_subclass(a, b))
    516         if result.size > 1:
    517             if m is not nomask:

<type 'exceptions.ValueError'>: shape mismatch: objects cannot be 
broadcast to a single shape



Do you know if this is caused by trying to use the new quiver.py in 
0.98.3?  Does my example before (copied below for convenience) work for you?

from pylab import *

X,Y = meshgrid( arange(0,1,.2),arange(0,1,.2) )
def yprime(x,y):
    return 1

U,V = meshgrid([1]*len(X), [1]*len(Y))

figure()
Q = quiver(X,Y,U, V, angles='xy')

# This is a solution to the differential equation y'=1, but it doesn't
# look like it because the slopes do not respect the aspect ratio of
# the plot.  What should happen is the arrows should point along the
# line.
plot([0,1],[0,1])

axis([0,1,0,0.5])

title("Slope Field for $dy/dx=1$")
show()


Thanks,

Jason