LinAlgError: Last 2 dimensions of the array must be square

Last 2 dimensions must be square

$ python - <<'PY'
import numpy as np
A = np.array([[1,2,3],[4,5,6]])
np.linalg.inv(A)
PY
Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
LinAlgError: Last 2 dimensions of the array must be square

Why this happens

Linear algebra routines like inv, eig, and solve require square matrices (n x n). Passing a non-square matrix triggers this error.

Fix

Ensure matrices are square. For rectangular problems use pseudo-inverse (np.linalg.pinv) or least-squares solvers (np.linalg.lstsq).

Wrong code

import numpy as np
A = np.array([[1,2,3],[4,5,6]])
np.linalg.inv(A)

Fixed code

import numpy as np
A = np.array([[1,2],[3,4]])
invA = np.linalg.inv(A)

# or use pseudo-inverse for rectangular matrices
B = np.array([[1,2,3],[4,5,6]])
pinvB = np.linalg.pinv(B)