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numpyのmatrixとmatは違うものなんですね

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この間numpyを使っていてハマったのですが、numpyのmatrixmatは違うものみたいです。本家のドキュメントを見てみるとmatmatrix(data, copy=False)と等価というふうに書いていて、コピーされないようになっているみたいです。これはどういうことかというと、

>>> import numpy as np
>>> m = np.matrix([[1.0, 2.0],[3.0, 4.0]])
>>> m
matrix([[ 1.,  2.],
        [ 3.,  4.]])
>>> a = np.matrix(m)
>>> a[0, 0] = 5.0
>>> a
matrix([[ 5.,  2.],
        [ 3.,  4.]])
>>> m
matrix([[ 1.,  2.],
        [ 3.,  4.]])
>>> #aを変更してもmは変わらない
>>> 
>>> b = np.mat(m)
>>> b[0, 0] = 6.0
>>> b
matrix([[ 6.,  2.],
        [ 3.,  4.]])
>>> m
matrix([[ 6.,  2.],
        [ 3.,  4.]])
>>> #bを変更するとmも変わる

ちょっとハマったので、書いてみました。

shiro-kuma
プログラミング言語はC, C++, pythonを主に使っています。 rustを勉強中
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