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      SUBROUTINE CTRTRIF( UPLO, DIAG, N, A, LDA, INFO )
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*
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*  -- LAPACK routine (version 3.0) --
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*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
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*     Courant Institute, Argonne National Lab, and Rice University
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*     September 30, 1994
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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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      COMPLEX            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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*  CTRTRI computes the inverse of a complex upper or lower triangular
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*  matrix A.
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*
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*  This is the Level 3 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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*          = 'U':  A is upper triangular;
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*          = 'L':  A is lower triangular.
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*
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*  DIAG    (input) CHARACTER*1
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*          = 'N':  A is non-unit triangular;
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*          = 'U':  A is 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) COMPLEX 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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*          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 = -i, the i-th argument had an illegal value
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*          > 0: if INFO = i, A(i,i) is exactly zero.  The triangular
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*               matrix is singular and its inverse can not be computed.
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*
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*  =====================================================================
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*
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*     .. Parameters ..
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      COMPLEX            ONE, ZERO
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      PARAMETER          ( ONE = ( 1.0E+0, 0.0E+0 ),
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     $                   ZERO = ( 0.0E+0, 0.0E+0 ) )
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*     ..
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*     .. Local Scalars ..
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      LOGICAL            NOUNIT, UPPER
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      INTEGER            J, JB, NB, NN
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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           CTRMM, CTRSM, CTRTI2, XERBLA
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*     ..
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*     .. Intrinsic Functions ..
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      INTRINSIC          MAX, MIN
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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( 'CTRTRI', -INFO )
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         RETURN
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      END IF
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*
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*     Quick return if possible
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*
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      IF( N.EQ.0 )
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     $   RETURN
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*
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*     Check for singularity if non-unit.
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*
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      IF( NOUNIT ) THEN
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         DO 10 INFO = 1, N
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            IF( A( INFO, INFO ).EQ.ZERO )
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     $         RETURN
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   10    CONTINUE
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         INFO = 0
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      END IF
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*
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*     Determine the block size for this environment.
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*
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      NB = 128
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      IF( NB.LE.1 .OR. NB.GE.N ) THEN
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*
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*        Use unblocked code
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*
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         CALL CTRTI2( UPLO, DIAG, N, A, LDA, INFO )
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      ELSE
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*
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*        Use blocked code
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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 20 J = 1, N, NB
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               JB = MIN( NB, N-J+1 )
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*
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*              Compute rows 1:j-1 of current block column
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*
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               CALL CTRMM( 'Left', 'Upper', 'No transpose', DIAG, J-1,
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     $                     JB, ONE, A, LDA, A( 1, J ), LDA )
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               CALL CTRSM( 'Right', 'Upper', 'No transpose', DIAG, J-1,
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     $                     JB, -ONE, A( J, J ), LDA, A( 1, J ), LDA )
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*
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*              Compute inverse of current diagonal block
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*
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               CALL CTRTI2( 'Upper', DIAG, JB, A( J, J ), LDA, INFO )
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   20       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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            NN = ( ( N-1 ) / NB )*NB + 1
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            DO 30 J = NN, 1, -NB
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               JB = MIN( NB, N-J+1 )
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               IF( J+JB.LE.N ) THEN
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*
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*                 Compute rows j+jb:n of current block column
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*
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                  CALL CTRMM( 'Left', 'Lower', 'No transpose', DIAG,
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     $                        N-J-JB+1, JB, ONE, A( J+JB, J+JB ), LDA,
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     $                        A( J+JB, J ), LDA )
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                  CALL CTRSM( 'Right', 'Lower', 'No transpose', DIAG,
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     $                        N-J-JB+1, JB, -ONE, A( J, J ), LDA,
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     $                        A( J+JB, J ), LDA )
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               END IF
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*
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*              Compute inverse of current diagonal block
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*
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               CALL CTRTI2( 'Lower', DIAG, JB, A( J, J ), LDA, INFO )
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   30       CONTINUE
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         END IF
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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 CTRTRI
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*
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      END