matplotlib限定colorbar的range

fig,ax=plt.subplots(figsize=(8,8))
cmap=plt.get_cmap('seismic')
cmap.set_bad(color='gray')
cb=ax.matshow(matdiff,cmap=cmap)
fig.colorbar(cb,ax=ax)
cb.set_clim(vmin=-1.0,vmax=1.0)
plt.show()