Matrix is singular to working precision

I was using Matlab 2010 and my code was working fine! I changed my windows and start using Matlab 2011b and I am getting this warning for the same code:

Matrix is singular to working precision.

I have absolutely no idea what could be the problem. In fact, I am running a power flow in Matlab and it used to converge with the same code before but now the load flow can not converge either.

Would be glad if somebody can give a hint :)

Answer 1

[Jan]

Without seeing the command, which causes the problem, it is impossible to guess the reason of the problem.

Are you really sure that you are running the same code with the same data?

Answer 2

[Ahmad Karnama]

Thanks Jan for your answer. This is the part of the code which generates the warning:

    %%evaluate Jacobian
    [dSbus_dVm, dSbus_dVa] = dSbus_dV(Ybus, V);

    j11 = real(dSbus_dVa([pv; pq], [pv; pq]));
    j12 = real(dSbus_dVm([pv; pq], pq));
    j21 = imag(dSbus_dVa(pq, [pv; pq]));
    j22 = imag(dSbus_dVm(pq, pq));

    J = [   j11 j12;
            j21 j22;    ];

    %%compute update step
    dx = -(J \ F);

and I think it causes the load flow not to converge! I thank you in advance for your help :)

[Jan]

I suggest to check, if F is near to singular on both Matlab versions.