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.
In mathematics, the term linear function refers to two distinct but related notions: 1  In calculus and related areas, a linear function is a polynomial function of degree zero or one, or is the zero polynomial. 2  In linear algebra and functional analysis, a linear function is a linear map.