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Convert sparse matrix to full matrix
A = full(S)
A = full(S)
converts a sparse matrix S
to full storage organization. If S
is a full matrix, it is left unchanged. If A
is full, issparse(A)
is 0
.
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 such computers, sparse(X)
requires less storage than full(X)
if the density, nnz/prod(size(X))
, is less than one third. Operations on sparse matrices, however, require more execution time per element than those on full matrices, so density should be considerably less than two-thirds before sparse storage is used.
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 Bytes Class A 200X200 320000 double array (logical) S 200X200 318432 sparse array (logical)
sparse
Create sparse matrix