Draw arrows on matplotlib figure directly
<p>I created a plot containing multiple subplots on a grid. The plots differ in two parameters, so I would like it to look like they ordered in a coordinate system.</p>

<p>I managed to plot lines using matplotlib.lines.Line2D() next to the subplots  directly on the figure. 
But I would prefer to have an arrow instead of a line to make it more clear.
(I can add the specific parameter values  using fig.text().)</p>

<p><a href="http://i.stack.imgur.com/qDl8F.png" rel="nofollow">I'd like the blue lines to be arrows</a></p>

<pre><code>import matplotlib as mpl
import matplotlib.pyplot as plt
import numpy as np
from itertools import product 

fig = plt.figure()
plotGrid = mpl.gridspec.GridSpec(2, 2)

x = np.linspace(0,10,10000)
y = [j* np.sin(x + i)  for i,j in product(range(2), range(1,3))]

for i in range(4):
    ax = plt.Subplot(fig, plotGrid[i])

    for sp in ax.spines.values():
        sp.set_visible(False)

    ax.plot(x,y[i], color = 'r')
    ax.set_xticks([])
    ax.set_yticks([])
    fig.add_subplot(ax)

all_axes = fig.get_axes()


#I would like these lines to be arrows  
blcorPosn = 0.08 #bottom corner position
l1 = mpl.lines.Line2D([blcorPosn,blcorPosn], [1, blcorPosn],
                      transform=fig.transFigure, fig)

l2 = mpl.lines.Line2D([blcorPosn, 1], [blcorPosn, blcorPosn],
                      transform=fig.transFigure, fig)

fig.lines.extend([l1, l2])
</code></pre>

<p>I'm not sure if this is the way to go. But I spend like a day on this by now and the only way I see so far to draw arrows is drawing them directly on an axes but thats not an option for me as far as I can see. </p>

<p>Also this is my first post here so advice on how to ask questions is highly appreciated. 
Thanks</p>