sprandsym

Purpose

Random sparse symmetric matrices.

Synopsis

R = sprandsym(S)
R = sprandsym(n,density)
R = sprandsym(n,density,rc)
R = sprandsym(n,density,rc,kind)

Description

R = sprandsym(S) is a symmetric random matrix whose lower triangle and diagonal have the same structure as S. Its elements are normally distributed, with mean 0 and variance 1.

R = sprandsym(n,density) is a symmetric random, n-by-n, sparse matrix with approximately density*n*n nonzeros; each entry is the sum of one or more normally distributed random samples, and (0 <= density <= 1).

R = sprandsym(n,density,rc) has a reciprocal condition number equal to rc. The distribution of entries is nonuniform; it is roughly symmetric about 0; all are in [-1,1].

If rc is a vector of length n, then R has eigenvalues rc. Thus, if rc is a positive (nonnegative) vector then R is a positive definite matrix. In either case, R is generated by random Jacobi rotations applied to a diagonal matrix with the given eigenvalues or condition number. It has a great deal of topological and algebraic structure.

R = sprandsym(n, density, rc, kind) is positive definite, where kind can be:

  • 1 to generate R by random Jacobi rotation of a positive definite diagonal matrix. R has the desired condition number exactly.
  • 2 to generate an R that is a shifted sum of outer products. R has the desired condition number only approximately, but has less structure.
  • 3 to generate an R that has the same structure as the matrix S and approximate condition number 1/rc. density is ignored.

    See Also

    sprandn
    

    (c) Copyright 1994 by The MathWorks, Inc.