@BenBolker, I tried these all now. still same error. how come in R, a matrix with non zero determinant is not invertible? – Mathica. Aug 23 at ... ... <看更多>

A sufficient condition for a symmetric n×n matrix C to be invertible is that the matrix is positive definite, i.e. ∀x∈Rn∖{0},xTCx>0. ... <看更多>

Let A be an n by n matrix. Then rank(A) = n iff A has an inverse. ... <看更多>