why does sem not run why doesn't sem run because it is non positive definite why does sem have definite singularity why does sem not run why doesn't sem test work why is sem definite non-negative why does sem fail why won't sem run why won't sem start what causes sem to not run why does sem run what is non-definite matrix why does sem don't work which matrix doesn't work in sem does sem consider singularity positive or negative what makes sem run what is the problem with sem why doesn't sem test why doesn't sem run why won't sem run