DGETRI(l) ) DGETRI(l)NAMEDGETRI - compute the inverse of a matrix using the LU factorization
computed by DGETRF
SYNOPSIS
SUBROUTINE DGETRI( N, A, LDA, IPIV, WORK, LWORK, INFO )
INTEGER INFO, LDA, LWORK, N
INTEGER IPIV( * )
DOUBLE PRECISION A( LDA, * ), WORK( * )
PURPOSEDGETRI computes the inverse of a matrix using the LU factorization com‐
puted by DGETRF. This method inverts U and then computes inv(A) by
solving the system inv(A)*L = inv(U) for inv(A).
ARGUMENTS
N (input) INTEGER
The order of the matrix A. N >= 0.
A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
On entry, the factors L and U from the factorization A = P*L*U
as computed by DGETRF. On exit, if INFO = 0, the inverse of
the original matrix A.
LDA (input) INTEGER
The leading dimension of the array A. LDA >= max(1,N).
IPIV (input) INTEGER array, dimension (N)
The pivot indices from DGETRF; for 1<=i<=N, row i of the matrix
was interchanged with row IPIV(i).
WORK (workspace/output) DOUBLE PRECISION array, dimension (LWORK)
On exit, if INFO=0, then WORK(1) returns the optimal LWORK.
LWORK (input) INTEGER
The dimension of the array WORK. LWORK >= max(1,N). For opti‐
mal performance LWORK >= N*NB, where NB is the optimal block‐
size 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 (output) 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 singu‐
lar and its inverse could not be computed.
LAPACK version 3.0 15 June 2000 DGETRI(l)