Feature #10074: [PATCH] generalize Vector#cross_product

• Status: Closed
• Assignee: marcandre (Marc-Andre Lafortune)
• Target version: 2.2.0

[gogotanaka (Kazuki Tanaka)]

Usually We use cross_product in only 3 dimensions.

Sometimes we want to handle cross_product in n-dimensions.

But I recognize Ruby should be not for mathematician but rubyist.

Ruby doesn't need too academic method.

So If you think it is too academic you can ignore my patches.

[gogotanaka (Kazuki Tanaka)]

Before

 Vector[1, 0, 0].cross_product Vector[0, 1, 0]
=> Vector[0, 0, 1]

Vector[1, 2].cross_product
=> ArgumentError: wrong number of arguments (0 for 1)

 Vector[3, 5, 2, 1].cross_product(Vector[4, 3, 1, 8], Vector[2, 9, 4, 3])
=> ArgumentError: wrong number of arguments (0 for 1)

After

 Vector[1, 0, 0].cross_product Vector[0, 1, 0]
=> Vector[0, 0, 1]

Vector[1, 2].cross_product
=> Vector[2, -1]

 Vector[3, 5, 2, 1].cross_product(Vector[4, 3, 1, 8], Vector[2, 9, 4, 3])
=> Vector[-16, 65, -139, 1]

This patch needs https://bugs.ruby-lang.org/issues/10072 and https://bugs.ruby-lang.org/issues/10073

gogo.

[hsbt (Hiroshi SHIBATA)]

• Category set to lib
• Status changed from Open to Assigned
• Assignee set to marcandre (Marc-Andre Lafortune)
• Target version set to 2.2.0

[marcandre (Marc-Andre Lafortune)]

I committed this change, with a couple of changes.

In particular, the sign was wrong for even dimensions. I changed it so we now have, for any n:

first, *middle, last = Matrix.identity(n).column_vectors
first.cross(*middle) == last

Thanks for this feature request!

[marcandre (Marc-Andre Lafortune)]

• Status changed from Assigned to Closed

[gogotanaka (Kazuki Tanaka)]

@Marc-Andre Lafortune

I'm really appreciate your help.
And your changes totally makes sense.

Thanks.