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.
His âBoolean algebraâ was actually a system of logic, with mathematical equations used to represent statements in logic. 1  Just as important was that it employed a binary approach in which the relationship between different mathematical quantities would be either true or false, 0 or 1.