Niharika, There could be multitude of reasons causing matrix singularity for power flow or optimal power flow problems. See FAQ 5 http://www.pserc.cornell.edu//matpower/#pfconvergence for some helpful tips on debugging this issue.
Shri From: Niharika Iter <niharika.iter2...@gmail.com<mailto:niharika.iter2...@gmail.com>> Reply-To: MATPOWER discussion forum <matpowe...@list.cornell.edu<mailto:matpowe...@list.cornell.edu>> Date: Thursday, June 25, 2015 at 11:23 PM To: "matpowe...@list.cornell.edu<mailto:matpowe...@list.cornell.edu>" <matpowe...@list.cornell.edu<mailto:matpowe...@list.cornell.edu>> Subject: Problem in finding inverse Dear Dr. Zimmerman, Sir I am dealing with Transmission Expansion Problem and i am facing problem in finding inverse for large systems such as South Brazilian 46 bus system or Brazillion North-Northeast 87 bus system ,as matrix is becoming singular. Please provide me feasible solution for this. With regards Niharika