Python - Add annotation in subplot imshow

Question

I would like to add some annotations on a figure with multiple subplots...On the figure below i would like to write something below the 2 right figures and at the left top. How can i do that?

I try with : ax3.text(0.1, 0.5, '$\sigma =$' resV.mean(), size=12, ha='center', va='center')

But that doesnt work, i would like to specify mean and standard deviation of the right plots

You can see a part of my code :

plt.close()
fig, axes = plt.subplots(nrows=2, ncols=3)

###Figures composante X
plt.tight_layout(pad=0.05, w_pad=0.001, h_pad=2.0)
ax1 = plt.subplot(231) # creates first axis
ax1.set_xticks([0,2000,500,1000,1500])
ax1.set_yticks([0,2000,500,1000,1500])
ax1.tick_params(labelsize=8) 
i1 = ax1.imshow(U,cmap='hot',extent=(X.min(),2000,Y.min(),2000), vmin=U.min(), vmax=U.max())
cb1=plt.colorbar(i1,ax=ax1,ticks=[U.min(),(U.min()+U.max())/2., U.max()],fraction=0.046, pad=0.04,format='%.2f')
cb1.ax.tick_params(labelsize=8)

ax1.set_title("$ \mathrm{Ux_{mes} \/ (pix)}$", y=1.05, fontsize=12)
ax2 = plt.subplot(232) # creates second axis
ax2.set_xticks([0,2000,500,1000,1500])
ax2.set_yticks([0,2000,500,1000,1500])
i2=ax2.imshow(UU,cmap='hot',extent=(X.min(),2000,Y.min(),2000), vmin=UU.min(), vmax=UU.max())
ax2.set_title("$\mathrm{Ux_{cal} \/ (pix)}$", y=1.05, fontsize=12)
ax2.set_xticklabels([])
ax2.set_yticklabels([])
cb2=plt.colorbar(i2,ax=ax2,fraction=0.046, pad=0.04,ticks=[UU.min(),(UU.min()+UU.max())/2.,UU.max()],format='%.2f')
cb2.ax.tick_params(labelsize=8)

ax3 = plt.subplot(233) # creates first axis
ax3.set_xticks([0,2000,500,1000,1500])
ax3.set_yticks([0,2000,500,1000,1500])
i3 = ax3.imshow(resU,cmap='hot',extent=(X.min(),2000,Y.min(),2000),vmin=0.,vmax=0.1)
ax3.imshow(scipy.ndimage.filters.gaussian_filter(masquey2, 3),cmap='hot',alpha=0.2,extent=(X.min(),2000,Y.min(),2000))
ax3.set_title("$\mathrm{\mid \/ Ux_{mes} - Ux_{cal}\mid \/ (pix)}$ ", y=1.05, fontsize=12)
cb3=plt.colorbar(i3,ax=ax3,fraction=0.046, pad=0.04,ticks=[0.,0.1],format='%.2f')
ax3.set_xticklabels([])
ax3.set_yticklabels([])
cb3.ax.tick_params(labelsize=8)
plt.gcf().tight_layout()

Answer 1

Q: But i dont know how to modify the number of significant digits.

A: Pre-process the value to be displayed round( 1.234567890123456e-2, 5 )

Answer 2

You can do this at format-time using the format string syntax

In [23]: 'sigma = {0:.5}'.format(np.pi)
Out[23]: 'sigma = 3.1416'

In [24]: 'sigma = {0:.3}'.format(np.pi)
Out[24]: 'sigma = 3.14'

In [25]: 'sigma = {0:.13}'.format(np.pi)
Out[25]: 'sigma = 3.14159265359'

Answer 3

Something like this should work alright given that 1,5 is the position you really want the text to appear:

ax3.text(1, 5, 'sigma = {0}'.format(resV.mean()), size=12, ha='center', va='center')