Allocate space for sparse matrix
S = spalloc(m,n,nz)
S = spalloc(m,n,nz) creates an all zero
sparse matrix S of size m-by-n
with room to hold nz nonzeros, where nz >= 1.
The matrix can then be generated column by column without requiring repeated storage
allocation as the number of nonzeros grows.
spalloc(m,n,nz) is shorthand for
sparse([],[],[],m,n,nz)
If you specify a value of 0 for nz, then
spalloc instead sets the value of nz to
1.
Use spalloc to initialize an
n-by-n empty sparse matrix with space for
3*n nonzeros. Then use a for-loop to fill in
the columns of S one at a time. The result is a tridiagonal matrix
with about 50% band density.
S = spalloc(n,n,3*n);
for j = 1:n
ind = [max(j-1,1) j min(j+1,n)];
S(:,j) = sparse(ind,1,round(rand(3,1)),n,1,3);
end