Section: Array Generation and Manipulations
y = nonzeros(x)
where x is the argument array.  The argument matrix may
be sparse as well as dense.
nonzeros on a sparse matrix.
--> a = rand(8); a(a>0.2) = 0;
--> A = sparse(a)
A = 
 4 1 0.150467
 6 1 0.119605
 7 1 0.0450479
 3 3 0.0592569
 4 3 0.185718
 3 4 0.064163
 7 4 0.196438
 8 4 0.103669
 4 5 0.160639
 2 6 0.0545093
 5 6 0.0226881
 8 6 0.0202693
 1 7 0.192362
 6 8 0.101635
 7 8 0.147931
--> nonzeros(A)
ans = 
    0.1505 
    0.1196 
    0.0450 
    0.0593 
    0.1857 
    0.0642 
    0.1964 
    0.1037 
    0.1606 
    0.0545 
    0.0227 
    0.0203 
    0.1924 
    0.1016 
    0.1479