The pivot indices.
If ipiv(k) > 0, then rows and columns k and ipiv(k) were
interchanged and D(k, k) is a '1 x 1' diagonal block.
If ipiv(k) = ipiv(k + 1) < 0, then rows and columns k+1 and
-ipiv(k) were interchanged and D(k:k+1, k:k+1) is a '2 x 2'
diagonal block.
The pivot indices. If ipiv(k) > 0, then rows and columns k and ipiv(k) were interchanged and D(k, k) is a '1 x 1' diagonal block. If ipiv(k) = ipiv(k + 1) < 0, then rows and columns k+1 and -ipiv(k) were interchanged and D(k:k+1, k:k+1) is a '2 x 2' diagonal block.