How to create a CRS structure in Matlab using val, rind, and cind.

I am needing to create a CRS structure (compressed row storage) in Matlab using val, rind, and cind for a singular matrix (not any matrix operations). I understand how the CRS structure works and what the output is meant to be. However, every time I try to try to code it, I cannot get it right. This is the reference article I am using to help me: http://www.netlib.org/utk/people/JackDongarra/etemplates/node373.html You can use any matrix as an example. I can adapt it to fit the problem I am working on.

I am new to Matlab, so this is where my inexperience kicks in. Any advice, tips, suggestions, etc. on just where to begin with the code would be greatly appreciated. Thank you.

Answer 1

[Karan Singh]

Hi Grace,

From what I understand, the goal is to create a MATLAB code that can generate the CRS structure for any given matrix.

Let's break down the steps to implement the CRS structure based on the reference article you provided:

• Initialize the CRS structure:
• Create three empty arrays:“val”,“rind”, and“cind”.
• “val”will store the non-zero values of the matrix.
• “rind”will store the row indices corresponding to the non-zero values.
• “cind”will store the column indices corresponding to the non-zero values.

• Traverse the matrix:
• Iterate over each row of the matrix.
• Within each row, iterate over each column.
• If the element at the current position is non-zero, store its value in the“val”array.
• Store the row index in the“rind”array.
• Store the column index in the“cind”array.

• Finalize the CRS structure:
• After traversing the entire matrix, store the total number of non-zero elements in a variable,“nnz”.
• Append a zero at the end of the“val”array.
• Append the value“nnz”at the end of the“rind”array.
• Append the value“nnz”at the end of the“cind”array.

Here's an example implementation:

% Example matrix 
matrix = [1 0 0 0; 0 2 0 0; 3 0 4 0; 0 0 0 5]; 

% Initialize CRS structure 
val = []; 
rind = []; 
cind = []; 

% Traverse the matrix 
[nrows, ncols] = size(matrix); 
nnz = 0; % Number of non-zero elements 

for i = 1:nrows 
    for j = 1:ncols 
        if matrix(i, j) ~= 0 
            val = [val matrix(i, j)]; 
            rind = [rind i]; 
            cind = [cind j]; 
            nnz = nnz + 1; 
        end 
    end 
end 

% Finalize CRS structure 
val = [val 0]; 
rind = [rind nnz]; 
cind = [cind nnz]; 

% Display the CRS structure 
disp("val: " + mat2str(val)) 
disp("rind: " + mat2str(rind)) 
disp("cind: " + mat2str(cind)) 

Attached below are some documentation links that you may find helpful:

• Sparse Matrix Operations - MATLAB & Simulink (mathworks.com)
• Matrices and Arrays - MATLAB & Simulink (mathworks.com)
• Array vs. Matrix Operations - MATLAB & Simulink (mathworks.com)
• Loops and Conditional Statements - MATLAB & Simulink (mathworks.com)

Hope this helps!

Karan Singh Khati