# SDP in CVX 3.0 fails due to Subscript indices must either be real positive integers or logicals

Hi,

I am solving an SDP problem in MATLAB.
When I use CVX 3.0, there is an error launched
"Subscript indices must either be real positive integers or logicals."
However, this error doesn’t occur when I use CVX 2.0 version or the same problem with different input data.

For a test of CVX 3.0, I attached my code

clear all; clc;

n = 2; m = 5; s = 5;
alpha = 1e-2;
R = [1 alpha alpha alpha alpha; …
alpha 1 alpha alpha alpha; …
alpha alpha 1 alpha alpha; …
alpha alpha alpha 1 alpha; …
alpha alpha alpha alpha 1];
w0 = zeros(m,1); w0( randi(m,1,s) ) = 1;
X0 = w0w0’;
Z0 = inv( ( 2 * X0 - ones(m,1) * w0’ - w0 * ones(1,m) + ones(m,1) * ones(1,m) ). R );
H = ones(m,n);

cvx_begin sdp
variable w(m);
variable X(m,m) symmetric;
variable Z(m,m) symmetric;
variable V(m,m) symmetric;
variable T(n,n) symmetric;
expression L1(m,m);
C = Z0; C0 = (2 * X0 - ones(m,1) * w0’ - w0 * ones(1,m));
L1 = C - C * ( ( 2 * X - ones(m,1) * w’ - w * ones(1,m) - C0 ).* R )* C;
expression L2(m,m);
L2 = X.* Z0 + X0.* Z - X0.* Z0;
minimize ( trace(T) + trace(V) );
subject to
trace(X) == s; %%% Linear
diag(X) - w == zeros(m,1); %% linear
[X, w; w.’, 1] >= 0; %%% Linear matrix ineq
[Z, eye(m); eye(m), (2X - ones(m,1) * w’ - w * ones(1,m) + ones(m,1) * ones(1,m)). R] >= 0; %%% LMI
Z - L1 <= V; %% LMI
V >= 0; %% LMI
L2 >= 0; %% LMI
[ (eye(n) + H’ * L2 * H), eye(n); …
eye(n), T] >= 0; %%% LMI
cvx_end

The CVX message is
"
Subscript indices must either be real positive integers or logicals.

Error in cvx_sdpt3>solve (line 211)
Avec{end}{end+1} = reshape( ( str_3 * str_2 ) * reshape( At(ti,:), nt, nv * m ), nt2 * nv, m );

Error in cvx_solve (line 399)
[ x, status, tprec, iters, y ] = shim.solve( At, b, c, cones, params );

Error in cvx_finish (line 57)
[ status, result, bound, iters, tol ] = cvx_solve;

Error in cvx_end (line 11)
evalin( ‘caller’, ‘cvx_finish’ );

Error in Test_CVX (line 39)
cvx_end
"

If we set alpha = 0, then the aforementioned code works for SDP and have the valid output.
"------------------------------------------------------------
Status: Solved
Optimal value (cvx_optval): +3.32964e-10
"

I am wondering the reason for this error. Can you fix it?

Thank you very much,

CVX 3.0beta has a lot of bugs. if CVX 2,.1 works for your problem, I recommend you use that.