Matrices is the plural of matrix.

Surely you must have done these. My daughter did them in 7th grade (I think).

it is just a case of multiplying a bunch of numbers in a 1 or 2-dimensional array with another bunch of numbers in another 1 or 2-dimensional array.

I just did a quick google and

this is about the best I could come up with. These web sites don't half know how to overcomplicate a simple process.

Numsgil can probably help more with the rest of the stuff. he is the math major around here.