SciPy.linalgでやりがちな（というか自分の踏んだ）ケアレスミスのメモ

逆行列 (Matrix inverse)

To obtain the matrix inverse, use linalg.pinv() instead of linalg.inv()

linalg.pinv の docs:
https://docs.scipy.org/doc/numpy/reference/generated/numpy.linalg.pinv.html
linalg.inv の docs:
https://docs.scipy.org/doc/numpy/reference/generated/numpy.linalg.inv.html
その他 Ref:
https://www.quora.com/What-is-the-difference-between-pinv-and-inv#:~:text=What%20is%20the%20difference%20between%20pinv%20and%20inv%3F,-ad%20b&text=pinv()%20function%20in%20OCTAVE,be%20an%20m*n%20matrix.

linalg.eig関数について

linalg.eig関数でeigenvectorは行列として縦方向に返ってくる
Docs: https://docs.scipy.org/doc/scipy/reference/generated/scipy.linalg.eig.html

When using eigval, eigvec = scipy.linalg.eig(), the returned eigenvectors are in the columns of eigvec.
Supposing we want the first eigenvalue & eigenvector pair of a matrix my_matrix,

import scipy.linalg as la
eigval, eigvec = la.eig(my_matrix)

then we need

eigval_pair1 = eigval[0]
eigvec_pair1 = eigvec[:,0]

and NOT

eigvec_pair1 = eigvec[0]