How to release zero elements in sparse matrix

Hi,

The Matlab document says sparse matrix does not release elements from memory when they are set to zero. Then how can I release the elements if they are zero?

For example:

>> a=sparse(ones(10,10));
>> nzmax(a)

ans =

     100

>> a(1:5,1:5)=0;
>> nzmax(a)

ans =

     100

>>

What I want is that nzmax(a) reports 75 since I don't want to waste the memory for 25 zeros. Is there any command I can use?

Thanks in advance!

Edit: Made the description of example clear.

Answer 1

[Azzi Abdelmalek]

Your example is not correct, what you should do is

a=ones(10,10);
nzmax(a)
a(1:5,1:5)=0
a=sparse(a)
nzmax(a)

Answer 2

[Andrei Bobrov]

nnz(a);

[Jimmy]

Hi Andrei,

Sorry I mean I want to really release the memory and that nzmax() reports 75. But thanks for the quick reply.

Jimmy

Answer 3

[Walter Roberson]

The examples of sparse show how to dissect and reconstruct a sparse matrix