It looks like a sparse matrix. These are useful when most of your matrix is filled with zeros - then the zeros don't need to be stored. It works and acts just like a full one most of the time (Different computing times for different functions will be noticeable though. Sometimes beneficial, sometimes not, depending on how the data looks and on the function).
Anyways, if you want to convert between the two you use the
sparse and the
sparse_mat = sparse(A); % if you want to make a "normal" matrix sparse full_mat = full(sparse_mat); % vice versa