SUBROUTINE SPOTRIF( 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 ..

      REAL               A( LDA, * )

*     ..

*

*  Purpose

*  =======

*

*  SPOTRI computes the inverse of a real symmetric positive definite

*  matrix A using the Cholesky factorization A = U**T*U or A = L*L**T

*  computed by SPOTRF.

*

*  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) REAL array, dimension (LDA,N)

*          On entry, the triangular factor U or L from the Cholesky

*          factorization A = U**T*U or A = L*L**T, as computed by

*          SPOTRF.

*          On exit, the upper or lower triangle of the (symmetric)

*          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           SLAUUM, STRTRI, 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( 'SPOTRI', -INFO )

         RETURN

      END IF

*

*     Quick return if possible

*

      IF( N.EQ.0 )

     $   RETURN

*

*     Invert the triangular Cholesky factor U or L.

*

      CALL STRTRI( UPLO, 'Non-unit', N, A, LDA, INFO )

      IF( INFO.GT.0 )

     $   RETURN

*

*     Form inv(U)*inv(U)' or inv(L)'*inv(L).

*

      CALL SLAUUM( UPLO, N, A, LDA, INFO )

*

      RETURN

*

*     End of SPOTRI

*

      END