full

Purpose

Convert sparse matrices to full storage class.

Synopsis

A = full(S)

Description

A = full(S) converts the storage of a matrix from sparse to full. If A is already full, full(A) returns A.

Let X be an m-by-n matrix with nz = nnz(X) nonzero entries. Then full(X) requires space to store m*n real numbers while sparse(X) requires space to store nz real numbers and (nz+n) integers. On most computers, a real number requires twice as much storage as an integer. On these computers, sparse(X) requires less storage than full(X)if the density, nnz/(m*n), is less than one third. Operations on sparse matrices, however, require more execution time per element than those on full matrices, so density is considerably less than two-thirds before sparse storage is used.

Examples

Here is an example of a sparse matrix with a density of about two-thirds. sparse(S) and full(S) require about the same number of bytes of storage.

S = sparse(rand(200,200) < 2/3);
A = full(S);
whos
          
Name      Size    Elements     Bytes    Density  Complex
          
  A    200 by 200    40000    320000       Full    No 
  S    200 by 200    26797    322364     0.6699    No

See Also

sparse

(c) Copyright 1994 by The MathWorks, Inc.