Science Memes

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identity theft (lemmy.dbzer0.com)

submitted 1 month ago by [email protected] to c/[email protected]

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[–] [email protected] 13 points 1 month ago* (last edited 2 weeks ago) (1 children)

That matrix of zeros with one in diagonal is called the matrix of identity.
It is famous because when doing multiplication on matrix or vector, it acts likes 1 on "normal" number:
x times 1 is x.
anyMatrix times Identity is anyMatrix.

[–] [email protected] 4 points 1 month ago (2 children)

Wouldn't you need to put anyMatrix first, since matrix multiplication isn't commutative?

[–] [email protected] 2 points 1 month ago (1 children)

You are right. I will correct it.

[–] [email protected] 1 points 1 month ago* (last edited 1 month ago) (1 children)

No I just tried it and I was wrong, it seems like it doesn't matter for the ID matrix specifically

[–] [email protected] 1 points 1 month ago

I need to freshen up on my linear algebra. I don't remember on which sense it goes but I think if you swap the factors, you'll have to you transpose the matrix x to keep the same result.

[–] [email protected] 1 points 1 month ago

Huh? Identity times anyMatrix is also anyMatrix. The matrix just has to have the right dimensions