Undefined function or variable 'cvx_begin'

Hi everyone! I'm trying to understand how does matlab work with the matrix factorization which related to my task now. I used this code to test for matrix factorization. And the code dont run because of a function. The warning told that: "Undefined function or variable 'cvx_begin'". What should I fix it? Have any professional matlaber help me? Thank you in advance. Here is my code:

% Generate data matrix A

rstate = rand();
m = 10; n = 10; k = 5;
A = rand(m,k)*rand(k,n);

% Initialize Y randomly

Y = rand(m,k);

% Perform alternating minimization

MAX_ITERS = 30;
residual = zeros(1,MAX_ITERS);
for iter = 1:MAX_ITERS
    cvx_begin quiet
        if mod(iter,2) == 1
            variable X(k,n)
            X >= 0;
        else
            variable Y(m,k)
            Y >= 0;
        end
        minimize(norm(A - Y*X,'fro'));
    cvx_end
    fprintf(1,'Iteration %d, residual norm %g\n',iter,cvx_optval);
    residual(iter) = cvx_optval;
end

% Plot residuals

plot(residual);
xlabel('Iteration Number');
ylabel('Residual Norm');

% Display results

disp( 'Original matrix:' );
disp( A );
disp( 'Left factor Y:' );
disp( Y );
disp( 'Right factor X:' );
disp( X );
disp( 'Residual A - Y * X:' );
disp( A - Y * X );
fprintf( 'Residual after %d iterations: %g\n', iter, cvx_optval );

[Adam Danz]

Please format your code so it can be copied, pasted, and examined. The idea here is to make as little work as possible for the people who are eager to help you.

Without looking at the code, I can say that your script is trying to execute a command named 'cvx_begin' and there is no variable in your work space named that and there is no function on your matlab path named that either.

[Adam]

Is it your code or someone else's? If it is yours then what do you expect cvx_begin to be? Why do you expect the code to know of it if you haven't defined it?

cvx_begin quiet

is a meaningless line. What is it supposed to be doing?

[Van Vy]

@Adam Danz: Thank you for suggesting. I wonder that why the code look so ugly even I edit many time. I know the reason already :)

@Adam This code I take from internet. The source here: http://web.cvxr.com/cvx/examples/html/nonneg_matrix_fact.html I'm a newbie, i can not code by myself yet, need to see and try to run code for testing. Because my topic is related with matrix factorization. Can you give a help?

Answer 1

[Steven Lord]

The cvx_begin function is not from any MathWorks-provided toolbox. I believe that it's part of this toolbox. You will need to download and install that toolbox to use that function.

[Van Vy]

Oh, really. It sounds good. I will try to find the toolbox. Thank you :)

[Adam Danz]

After you download the toolbox to your Matlab folder you'll have to make sure that the directory that stores the toolbox is on your Matlab path.

Judging from the code you provided, there might be additional problems so feel free to return for help.