```      SUBROUTINE CTRTRI( UPLO, DIAG, N, A, LDA, INFO )
*
*  -- LAPACK routine (version 3.1) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
CHARACTER          DIAG, UPLO
INTEGER            INFO, LDA, N
*     ..
*     .. Array Arguments ..
COMPLEX            A( LDA, * )
*     ..
*
*  Purpose
*  =======
*
*  CTRTRI computes the inverse of a complex upper or lower triangular
*  matrix A.
*
*  This is the Level 3 BLAS version of the algorithm.
*
*  Arguments
*  =========
*
*  UPLO    (input) CHARACTER*1
*          = 'U':  A is upper triangular;
*          = 'L':  A is lower triangular.
*
*  DIAG    (input) CHARACTER*1
*          = 'N':  A is non-unit triangular;
*          = 'U':  A is unit triangular.
*
*  N       (input) INTEGER
*          The order of the matrix A.  N >= 0.
*
*  A       (input/output) COMPLEX array, dimension (LDA,N)
*          On entry, the triangular matrix A.  If UPLO = 'U', the
*          leading N-by-N upper triangular part of the array A contains
*          the upper triangular matrix, and the strictly lower
*          triangular part of A is not referenced.  If UPLO = 'L', the
*          leading N-by-N lower triangular part of the array A contains
*          the lower triangular matrix, and the strictly upper
*          triangular part of A is not referenced.  If DIAG = 'U', the
*          diagonal elements of A are also not referenced and are
*          assumed to be 1.
*          On exit, the (triangular) inverse of the original matrix, in
*          the same storage format.
*
*  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, A(i,i) is exactly zero.  The triangular
*               matrix is singular and its inverse can not be computed.
*
*  =====================================================================
*
*     .. Parameters ..
COMPLEX            ONE, ZERO
PARAMETER          ( ONE = ( 1.0E+0, 0.0E+0 ),
\$                   ZERO = ( 0.0E+0, 0.0E+0 ) )
*     ..
*     .. Local Scalars ..
LOGICAL            NOUNIT, UPPER
INTEGER            J, JB, NB, NN
*     ..
*     .. External Functions ..
LOGICAL            LSAME
INTEGER            ILAENV
EXTERNAL           LSAME, ILAENV
*     ..
*     .. External Subroutines ..
EXTERNAL           CTRMM, CTRSM, CTRTI2, XERBLA
*     ..
*     .. Intrinsic Functions ..
INTRINSIC          MAX, MIN
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters.
*
INFO = 0
UPPER = LSAME( UPLO, 'U' )
NOUNIT = LSAME( DIAG, 'N' )
IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
INFO = -1
ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
INFO = -2
ELSE IF( N.LT.0 ) THEN
INFO = -3
ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
INFO = -5
END IF
IF( INFO.NE.0 ) THEN
CALL XERBLA( 'CTRTRI', -INFO )
RETURN
END IF
*
*     Quick return if possible
*
IF( N.EQ.0 )
\$   RETURN
*
*     Check for singularity if non-unit.
*
IF( NOUNIT ) THEN
DO 10 INFO = 1, N
IF( A( INFO, INFO ).EQ.ZERO )
\$         RETURN
10    CONTINUE
INFO = 0
END IF
*
*     Determine the block size for this environment.
*
NB = ILAENV( 1, 'CTRTRI', UPLO // DIAG, N, -1, -1, -1 )
IF( NB.LE.1 .OR. NB.GE.N ) THEN
*
*        Use unblocked code
*
CALL CTRTI2( UPLO, DIAG, N, A, LDA, INFO )
ELSE
*
*        Use blocked code
*
IF( UPPER ) THEN
*
*           Compute inverse of upper triangular matrix
*
DO 20 J = 1, N, NB
JB = MIN( NB, N-J+1 )
*
*              Compute rows 1:j-1 of current block column
*
CALL CTRMM( 'Left', 'Upper', 'No transpose', DIAG, J-1,
\$                     JB, ONE, A, LDA, A( 1, J ), LDA )
CALL CTRSM( 'Right', 'Upper', 'No transpose', DIAG, J-1,
\$                     JB, -ONE, A( J, J ), LDA, A( 1, J ), LDA )
*
*              Compute inverse of current diagonal block
*
CALL CTRTI2( 'Upper', DIAG, JB, A( J, J ), LDA, INFO )
20       CONTINUE
ELSE
*
*           Compute inverse of lower triangular matrix
*
NN = ( ( N-1 ) / NB )*NB + 1
DO 30 J = NN, 1, -NB
JB = MIN( NB, N-J+1 )
IF( J+JB.LE.N ) THEN
*
*                 Compute rows j+jb:n of current block column
*
CALL CTRMM( 'Left', 'Lower', 'No transpose', DIAG,
\$                        N-J-JB+1, JB, ONE, A( J+JB, J+JB ), LDA,
\$                        A( J+JB, J ), LDA )
CALL CTRSM( 'Right', 'Lower', 'No transpose', DIAG,
\$                        N-J-JB+1, JB, -ONE, A( J, J ), LDA,
\$                        A( J+JB, J ), LDA )
END IF
*
*              Compute inverse of current diagonal block
*
CALL CTRTI2( 'Lower', DIAG, JB, A( J, J ), LDA, INFO )
30       CONTINUE
END IF
END IF
*
RETURN
*
*     End of CTRTRI
*
END

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