import numpy as np
rows = np.array([[1., 2., 8.], [2., 4., 6.], [3., 6., 4.], [4., 8., 2.]])
matrix = np.corrcoef(rows, rowvar=False)
assert matrix.shape == (3, 3)
assert np.allclose(matrix, [[1,1,-1],[1,1,-1],[-1,-1,1]], atol=1e-12)
print("Three-variable matrix: first two move together; third moves oppositely")