CODEWITHSUNDEEP
pythonnumpyvector
Ferdinando Randisi
Ferdinando Randisi

Reputation: 4388

How can I compute the inverse cross product of a vector in numpy?

How can I perform the inverse cross product in numpy?

That is, given two numpy arrays b and c, how can I find a such that

a.cross(b) == c

EDIT: Could whoever downvoted please let me know what they didn't like it, so that I can learn from their opinion? I asked the question because I didn't easily find an answer anywhere. Turns out the question is mathematically ill-defined (as people pointed out), but from now on if people look it up here this answer will show up and they'll know that quickly and easily.

Upvotes: 3

Views: 2151

Answers (2)

Adam P.
Adam P.

Reputation: 75

There is no function native to numpy that will arrive at the solution you're looking for. You may have better luck asking the question here.

There seems to be a problem with the question as well. From what I know of linear algebra, solving for 'a' wouldn't yield a unique solution unless certain conditions are met.

See this answer over at the math stack exchange for more information.

Upvotes: 1

Ewoud
Ewoud

Reputation: 751

There only exists a solution if a and c are orthogonal, and the solution is not unique.

Then, a = np.cross(b,c)/np.dot(b,b)+t*b is a solution for all t.

See this question on Math SE: https://math.stackexchange.com/questions/32600/whats-the-opposite-of-a-cross-product

Upvotes: 3

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