Plot the sparsity pattern of arrays
import matplotlib.pyplot as plt
import numpy as np
fig, axs = plt.subplots(2, 2)
ax1 = axs[0, 0]
ax2 = axs[0, 1]
ax3 = axs[1, 0]
ax4 = axs[1, 1]
x = np.random.randn(20, 20)
x[5, :] = 0.
x[:, 12] = 0.
ax1.spy(x, markersize=5)
ax2.spy(x, precision=0.1, markersize=5)
ax3.spy(x)
ax4.spy(x, precision=0.1)
plt.show()