How to save a sparse matrix to mat file in matlab

Question

I want to save two sparse matrix Y and R to a mat file. However, when I run the following code, I found out that the twomatrices.mat contains two full matrices instead of sparse matrices. Do does .mat file only allow full matrices to be included?

save('twomatrices.mat', 'Y', 'R');

Answer 1

Be sure that you actually create sparse matrices: e.g., the following code snippet works fine and stores the matrices as sparse double matrices:

n = 5;
Y = sparse(1:n,1:n,1);
R = sparse(1:n,1:n,2);
save('twomatrices.mat', 'Y', 'R');

clear
load('twomatrices.mat')
Y


Y =

   (1,1)        1
   (2,2)        1
   (3,3)        1
   (4,4)        1
   (5,5)        1