cpotri.f

          SUBROUTINE CPOTRI( UPLO, N, A, LDA, INFO )
    *
    *  -- LAPACK routine (version 3.1) --
    *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
    *     November 2006
    *
    *     .. Scalar Arguments ..
          CHARACTER          UPLO
          INTEGER            INFO, LDA, N
    *     ..
    *     .. Array Arguments ..
          COMPLEX            A( LDA, * )
    *     ..
    *
    *  Purpose
    *  =======
    *
    *  CPOTRI computes the inverse of a complex Hermitian positive definite
    *  matrix A using the Cholesky factorization A = U**H*U or A = L*L**H
    *  computed by CPOTRF.
    *
    *  Arguments
    *  =========
    *
    *  UPLO    (input) CHARACTER*1
    *          = 'U':  Upper triangle of A is stored;
    *          = 'L':  Lower triangle of A is stored.
    *
    *  N       (input) INTEGER
    *          The order of the matrix A.  N >= 0.
    *
    *  A       (input/output) COMPLEX array, dimension (LDA,N)
    *          On entry, the triangular factor U or L from the Cholesky
    *          factorization A = U**H*U or A = L*L**H, as computed by
    *          CPOTRF.
    *          On exit, the upper or lower triangle of the (Hermitian)
    *          inverse of A, overwriting the input factor U or L.
    *
    *  LDA     (input) INTEGER
    *          The leading dimension of the array A.  LDA >= max(1,N).
    *
    *  INFO    (output) INTEGER
    *          = 0:  successful exit
    *          < 0:  if INFO = -i, the i-th argument had an illegal value
    *          > 0:  if INFO = i, the (i,i) element of the factor U or L is
    *                zero, and the inverse could not be computed.
    *
    *  =====================================================================
    *
    *     .. External Functions ..
          LOGICAL            LSAME
          EXTERNAL           LSAME
    *     ..
    *     .. External Subroutines ..
          EXTERNAL           CLAUUM, CTRTRI, XERBLA
    *     ..
    *     .. Intrinsic Functions ..
          INTRINSIC          MAX
    *     ..
    *     .. Executable Statements ..
    *
    *     Test the input parameters.
    *
          INFO = 0
          IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
             INFO = -1
          ELSE IF( N.LT.0 ) THEN
             INFO = -2
          ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
             INFO = -4
          END IF
          IF( INFO.NE.0 ) THEN
             CALL XERBLA( 'CPOTRI', -INFO )
             RETURN
          END IF
    *
    *     Quick return if possible
    *
          IF( N.EQ.0 )
         $   RETURN
    *
    *     Invert the triangular Cholesky factor U or L.
    *
          CALL CTRTRI( UPLO, 'Non-unit', N, A, LDA, INFO )
          IF( INFO.GT.0 )
         $   RETURN
    *
    *     Form inv(U)*inv(U)' or inv(L)'*inv(L).
    *
          CALL CLAUUM( UPLO, N, A, LDA, INFO )
    *
          RETURN
    *
    *     End of CPOTRI
    *
          END