Matrix multiplication refresher: develop your intuition for matrix multiplication! (Or, "matrix multiplication for dummies")

matrix_multiplication_refresher.md

A refresher on matrix multiplication. Because your math classes were years ago. Here's the order I recommend:

1. TED-Ed video — How to organize, add and multiply matrices - Bill Shillito (only 5 minutes)
2. betterexplained.com — "An Intuitive Guide to Linear Algebra" by Kalid Azad
3. mathinsight.org: "Matrices and linear transformations"
4. Read some of the answers on math.stackexchange.com. You've been studying the general definition of matrix multiplication. You may wonder: "Are there other ways to define the product of two matrices?" These resources will answer, yes, there are other ways, but also explain why this general definition is the standard way.
   1. What is the intuitive way of thinking about multiplication of matrices?
   2. Matrix multiplication: interpreting and understanding the process.

There's also Khan Academy's lessons but I haven't tried them. Got what I needed from the other resources. There's also-also Prof. Andrew Ng's refresher in his Machine Learning course ... why I am brushing up here (though it's not strictly necessary to understand this stuff for the sake of the class). These resources all complement each other.

Last note: I called out every site/publication by name, because they all have more to offer. Check 'em out.

Other things ... may pull up into the above, need to digest it more.

• http://www.math.nyu.edu/~neylon/linalgfall04/project1/jme/index
• http://blog.stata.com/2011/03/03/understanding-matrices-intuitively-part-1/
• insightful comment: http://aha.betterexplained.com/t/an-intuitive-guide-to-linear-algebra/234/19
• http://mathworld.wolfram.com/RotationMatrix.html
• reference guide (bookmark it): http://mathworld.wolfram.com/topics/Matrices.html

If you are in the course, don't forget about the Linear Algebra review on the wiki (requires login).

As for Octave/MATLAB ... resources abound ... but sometimes people forget about Learn X in Y Minutes. https://learnxinyminutes.com/docs/matlab/ is very very helpful (for programmers)

http://matrixmultiplication.xyz/ interactive, this would have been nice to see sooner!

This can help too: https://kishorepv.github.io/Matrix-Multiplication/