Random sparse matrices.

  R = SPRANDN(S) has the same sparsity structure as S, but normally

      distributed random entries.

  R = SPRANDN(m,n,density) is a random, m-by-n, sparse matrix with 

      approximately density*m*n normally distributed nonzero entries.

  R = SPRANDN(m,n,density,rc) also has reciprocal condition number

      approximately equal to rc.  R is constructed from a sum of

      matrices of rank one. 



      If rc is a vector of length lr <= min(m,n), then R has 

      rc as its first lr singular values, all others are zero.

      In this case, R is generated by random plane rotations

      applied to a diagonal matrix with the given singular values

      It has a great deal of topological and algebraic structure.