1727, from L. sparsus "scattered," pp. of spargere "to scatter, spread," from PIE base *(s)pregh- "to jerk, scatter" (cf. Skt. parjanya- "rain, rain god," Avestan fra-sparega "branch, twig," lit. "that which is jerked off a tree," O.N. freknur "freckles," Swed. dial. sprygg "brisk, active," Lith. sprogti "shoot, bud," O.Ir. arg "a drop").
A sparse matrix (or vector, or array) is one in which most of the elements are zero. If storage space is more important than access speed, it may be preferable to store a sparse matrix as a list of (index, value) pairs or use some kind of hash scheme or associative memory. (1995-01-16)