Matrices in Codea - a blog(ish) post

General
1

I’ve written a blog(ish) post about matrices in Codea. Having seen a fair amount of confusion about them, I thought I’d like to set things straight. There are a few subtleties about order and so forth.

You can read it at http://loopspace.mathforge.org/discussion/13/matrices-in-codea. Although the website uses a forum software, it’s not a forum. I suggest comments and discussions be here.

This was being written while certain recent conversations here about matrices were happening. These inspired various parts.

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I read this article. It’s really good! It gets a bit heady in the middle, so read, take a short break, then go back to it! Great article, Andrew!

3

Thanks!

Which bits are “heady”? I tried to keep the maths to a minimum but it’s a bit tricky to do.

4

Thanks for writing this, @Andrew_Stacey! I will need to play with the examples to better understand it. I’ve used quaternions before for 3D rotations, but couldn’t say I understand them fully. Are they applicable to Codea for specifying rotations?

5

@Fred I use quaternions for handling rotations - I find them much easier to handle and manipulate than rotation matrices. When writing my shape explorer, I wrote a library for dealing with quaternions: http://www.math.ntnu.no/~stacey/code/CodeaLibrary/Quaternion.lua. In particular, it has a function for converting a quaternion to a matrix suitable for using in modelMatrix().

I could write a follow-up post on quaternions if there’s interest.

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Please do, quarternions are of interest as they seem ‘simpler’ to deal with.

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Yes @Andrew_Stacey, I enjoy reading your explanations and would be interested in reading about what you’ve done with quaternions for Codea.

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The sub article ‘saving the result’ starts to go beyond easy explanation. By the time someone gets there, their head is buzzing and they should take a break before trying to read all that math…

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My intention was that you don’t have to read the more maths-y bits - you can just assume the result. I just don’t like it when something says “This is what you need to do” without giving any explanation. If it provides explanation then I can choose to skip it or not, but if it doesn’t then I don’t have a choice.

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So…how is that quarternions article going? I am working on artillery fire, seems that quats would be good for that!