f = spfun('function',S)
f = spfun('function',S) evaluates function(S) on the nonzero elements of S. function must be the name of a function, usually defined in an M-file, which can accept a matrix argument, S, and evaluate the function at each element of S.
f = spfun('exp',S) has the same sparsity pattern as S (except for underflow), whereas exp(S) has 1s where S has 0s.
(c) Copyright 1994 by The MathWorks, Inc.