solving linear system with highly sparse matrices

Hi I want to solve a linear system Ax=b, with A and b very sparse and big. Right now my code is in the testing so the matrices are of the order of only a few hundreds, but eventually it's going to be bigger. for example, for the system of order 172 with the condition number 3.7987e+03 I tried pcg in matlab, but I am getting this error:

"pcg stopped at iteration 3 without converging to the desired tolerance 1e-06 because a scalar quantity became too small or too large to continue computing. The iterate returned (number 0) has relative residual 1 "

What other method I can try.. I dont want to rely on linsolve or "/" since I dont think these methods can be trusted for the bigger matrices. Please correct me if I am wrong. Thanks

Answer 1

[Andrew Newell]

In this previous post, a backslash is easily able to deal with a system of order 300,000. The key is defining your sparse matrix efficiently.