Question

I have data saved from each loop run and it looks like this.

val =

   (1,1)      16.0000

   (9,1)       0.0017

  (10,1)       0.0040

  (11,1)       0.0049

  (12,1)       0.0048

  (13,1)       0.0043

The matrix is 50×50, however only the cells that contain the specific element are showed in this save.

I know that those are the values and their corresponding locations.

I want to know what this format is and how can I count the the number cells shown this way quickly.

Answer 1

This is a sparse matrix, as @Oli already said correctly. I will try to elaborate a little bit.

You create it with the following commands:

 s = sparse(zeros(13,13));
 s(1,1) = 16;
 s(9,1) = 0.0017;
 s(10,1) = 0.0040;
 ...

Convert it back to full matrix by using full command:

 f = full(s);

And it you want to count the number of entries, use nnz. It counts the number of non zero entries:

 z = nnz(s);