Extracting non-zero values from a matrix and storing its row,column index and its associated value.

Could anyone help me build and correct my code which aims to only save the non-zero elements of an arbitrary square matrix and its index? Basically I need to write a script that does the same function as 'sparse' in MATLAB.

I want to have the same output as if I were to write sparse(A), where A is my matrix.

Here is my attempt:

 `%Consider a 3x3 matrix

A=[ 0 0 9 ;-1 8 0;0 -5 0 ];
n=3; %size of matrix

%initialise following arrays:
RI= zeros(n,1); %row index
CI = zeros(n,1); %column index
V = zeros(n,1); %value in the matrix
for k = 1:n %row 1 to n
    for j = 1:n %column 1 to n
      if A(k,j)~=0
        RI(k)=k;
        CI(j)=j;
        V(k,j)=A(k,j);
      end
    end 
end`

[Chintan Patel]

Try this commad:

B = nonzeros(A)

This would extract all the non-zero elements of matrix A :)

Answer 1

[Image Analyst]

Try this

A = [0, 0, 9; -1, 8, 0; 0, -5, 0];
nonZeroIndices = A ~= 0;
% Extract those non-zero values into a new variable called output:
output = A(nonZeroIndices)
% Determine their row and column indices:
[rows, columns] = find(nonZeroIndices)

[Guillaume]

Even simpler:

[rows, colums, values] = find(A)

[Image Analyst]

OK, cool. I never even knew find() had a third output.