SGETRI computes the inverse of a matrix using the LU factorization


 computed by SGETRF.


 This method inverts U and then computes inv(A) by solving the system


 inv(A)*L = inv(U) for inv(A).

N

          N is INTEGER


          The order of the matrix A.  N >= 0.

A

          A is REAL array, dimension (LDA,N)


          On entry, the factors L and U from the factorization


          A = P*L*U as computed by SGETRF.


          On exit, if INFO = 0, the inverse of the original matrix A.

LDA

          LDA is INTEGER


          The leading dimension of the array A.  LDA >= max(1,N).

IPIV

          IPIV is INTEGER array, dimension (N)


          The pivot indices from SGETRF; for 1<=i<=N, row i of the


          matrix was interchanged with row IPIV(i).

WORK

          WORK is REAL array, dimension (MAX(1,LWORK))


          On exit, if INFO=0, then WORK(1) returns the optimal LWORK.

LWORK

          LWORK is INTEGER


          The dimension of the array WORK.  LWORK >= max(1,N).


          For optimal performance LWORK >= N*NB, where NB is


          the optimal blocksize returned by ILAENV.


          If LWORK = -1, then a workspace query is assumed; the routine


          only calculates the optimal size of the WORK array, returns


          this value as the first entry of the WORK array, and no error


          message related to LWORK is issued by XERBLA.

INFO

          INFO is INTEGER


          = 0:  successful exit


          < 0:  if INFO = -i, the i-th argument had an illegal value


          > 0:  if INFO = i, U(i,i) is exactly zero; the matrix is


                singular and its inverse could not be computed.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016