fix a sign error in 3x3 characteristic polynomial
fix a sign error in 3x3 characteristic polynomial

YetAnotherMinion/core,YetAnotherMinion/core,YetAnotherMinion/core,yangf4/core,yangf4/core,YetAnotherMinion/core,yangf4/core,yangf4/core,yangf4/core,YetAnotherMinion/core