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      SUBROUTINE DTRTI2F( UPLO, DIAG, N, A, LDA, INFO )
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*
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*  -- LAPACK routine (version 3.1) --
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*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
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*     November 2006
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*
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*     .. Scalar Arguments ..
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      CHARACTER          DIAG, UPLO
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      INTEGER            INFO, LDA, N
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*     ..
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*     .. Array Arguments ..
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      DOUBLE PRECISION   A( LDA, * )
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*     ..
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*
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*  Purpose
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*  =======
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*
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*  DTRTI2 computes the inverse of a real upper or lower triangular
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*  matrix.
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*
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*  This is the Level 2 BLAS version of the algorithm.
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*
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*  Arguments
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*  =========
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*
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*  UPLO    (input) CHARACTER*1
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*          Specifies whether the matrix A is upper or lower triangular.
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*          = 'U':  Upper triangular
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*          = 'L':  Lower triangular
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*
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*  DIAG    (input) CHARACTER*1
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*          Specifies whether or not the matrix A is unit triangular.
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*          = 'N':  Non-unit triangular
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*          = 'U':  Unit triangular
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*
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*  N       (input) INTEGER
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*          The order of the matrix A.  N >= 0.
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*
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*  A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
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*          On entry, the triangular matrix A.  If UPLO = 'U', the
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*          leading n by n upper triangular part of the array A contains
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*          the upper triangular matrix, and the strictly lower
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*          triangular part of A is not referenced.  If UPLO = 'L', the
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*          leading n by n lower triangular part of the array A contains
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*          the lower triangular matrix, and the strictly upper
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*          triangular part of A is not referenced.  If DIAG = 'U', the
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*          diagonal elements of A are also not referenced and are
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*          assumed to be 1.
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*
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*          On exit, the (triangular) inverse of the original matrix, in
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*          the same storage format.
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*
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*  LDA     (input) INTEGER
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*          The leading dimension of the array A.  LDA >= max(1,N).
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*
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*  INFO    (output) INTEGER
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*          = 0: successful exit
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*          < 0: if INFO = -k, the k-th argument had an illegal value
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*
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*  =====================================================================
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*
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*     .. Parameters ..
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      DOUBLE PRECISION   ONE
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      PARAMETER          ( ONE = 1.0D+0 )
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*     ..
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*     .. Local Scalars ..
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      LOGICAL            NOUNIT, UPPER
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      INTEGER            J
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      DOUBLE PRECISION   AJJ
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*     ..
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*     .. External Functions ..
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      LOGICAL            LSAME
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      EXTERNAL           LSAME
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*     ..
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*     .. External Subroutines ..
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      EXTERNAL           DSCAL, DTRMV, XERBLA
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*     ..
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*     .. Intrinsic Functions ..
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      INTRINSIC          MAX
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*     ..
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*     .. Executable Statements ..
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*
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*     Test the input parameters.
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*
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      INFO = 0
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      UPPER = LSAME( UPLO, 'U' )
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      NOUNIT = LSAME( DIAG, 'N' )
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      IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
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         INFO = -1
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      ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
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         INFO = -2
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      ELSE IF( N.LT.0 ) THEN
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         INFO = -3
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      ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
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         INFO = -5
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      END IF
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      IF( INFO.NE.0 ) THEN
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         CALL XERBLA( 'DTRTI2', -INFO )
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         RETURN
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      END IF
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*
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      IF( UPPER ) THEN
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*
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*        Compute inverse of upper triangular matrix.
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*
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         DO 10 J = 1, N
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            IF( NOUNIT ) THEN
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               A( J, J ) = ONE / A( J, J )
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               AJJ = -A( J, J )
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            ELSE
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               AJJ = -ONE
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            END IF
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*
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*           Compute elements 1:j-1 of j-th column.
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*
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            CALL DTRMV( 'Upper', 'No transpose', DIAG, J-1, A, LDA,
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     $                  A( 1, J ), 1 )
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            CALL DSCAL( J-1, AJJ, A( 1, J ), 1 )
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   10    CONTINUE
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      ELSE
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*
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*        Compute inverse of lower triangular matrix.
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*
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         DO 20 J = N, 1, -1
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            IF( NOUNIT ) THEN
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               A( J, J ) = ONE / A( J, J )
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               AJJ = -A( J, J )
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            ELSE
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               AJJ = -ONE
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            END IF
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            IF( J.LT.N ) THEN
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*
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*              Compute elements j+1:n of j-th column.
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*
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               CALL DTRMV( 'Lower', 'No transpose', DIAG, N-J,
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     $                     A( J+1, J+1 ), LDA, A( J+1, J ), 1 )
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               CALL DSCAL( N-J, AJJ, A( J+1, J ), 1 )
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            END IF
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   20    CONTINUE
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      END IF
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*
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      RETURN
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*
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*     End of DTRTI2
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*
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      END