sand dollar. n. 1. Any of various thin circular echinoderms of the order Clypeasteroida, especially Echinarachnius parma, of coastal northern Atlantic and Pacific waters, having a covering of short movable spines.
One reason why linear algebra is very useful is that linear transforms of normal variables are normal. If x ~ N(a, A), then Bx+b ~ N(Ba+b, BABT). In a way, when everything is linear and normal, everything is nice and analytically tractable.
Linear Algebra, apparently, is the tool you would use to calculate these problems. (I say apparently because I have never used it. I am not a mathematician.) One definition of Linear Algebra I ran across says it is the branch of mathematics concerning vector spaces and linear mapping between such spaces. So, what are vector spaces?