ctptrs.f

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*> \brief \b CTPTRS
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
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*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       SUBROUTINE CTPTRS( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
*
*       .. Scalar Arguments ..
*       CHARACTER          DIAG, TRANS, UPLO
*       INTEGER            INFO, LDB, N, NRHS
*       ..
*       .. Array Arguments ..
*       COMPLEX            AP( * ), B( LDB, * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> CTPTRS solves a triangular system of the form
*>
*>    A * X = B,  A**T * X = B,  or  A**H * X = B,
*>
*> where A is a triangular matrix of order N stored in packed format,
*> and B is an N-by-NRHS matrix.  A check is made to verify that A is
*> nonsingular.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] UPLO
*> \verbatim
*>          UPLO is CHARACTER*1
*>          = 'U':  A is upper triangular;
*>          = 'L':  A is lower triangular.
*> \endverbatim
*>
*> \param[in] TRANS
*> \verbatim
*>          TRANS is CHARACTER*1
*>          Specifies the form of the system of equations:
*>          = 'N':  A * X = B     (No transpose)
*>          = 'T':  A**T * X = B  (Transpose)
*>          = 'C':  A**H * X = B  (Conjugate transpose)
*> \endverbatim
*>
*> \param[in] DIAG
*> \verbatim
*>          DIAG is CHARACTER*1
*>          = 'N':  A is non-unit triangular;
*>          = 'U':  A is unit triangular.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The order of the matrix A.  N >= 0.
*> \endverbatim
*>
*> \param[in] NRHS
*> \verbatim
*>          NRHS is INTEGER
*>          The number of right hand sides, i.e., the number of columns
*>          of the matrix B.  NRHS >= 0.
*> \endverbatim
*>
*> \param[in] AP
*> \verbatim
*>          AP is COMPLEX array, dimension (N*(N+1)/2)
*>          The upper or lower triangular matrix A, packed columnwise in
*>          a linear array.  The j-th column of A is stored in the array
*>          AP as follows:
*>          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
*>          if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j<=i<=n.
*> \endverbatim
*>
*> \param[in,out] B
*> \verbatim
*>          B is COMPLEX array, dimension (LDB,NRHS)
*>          On entry, the right hand side matrix B.
*>          On exit, if INFO = 0, the solution matrix X.
*> \endverbatim
*>
*> \param[in] LDB
*> \verbatim
*>          LDB is INTEGER
*>          The leading dimension of the array B.  LDB >= max(1,N).
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*>          INFO is INTEGER
*>          = 0:  successful exit
*>          < 0:  if INFO = -i, the i-th argument had an illegal value
*>          > 0:  if INFO = i, the i-th diagonal element of A is zero,
*>                indicating that the matrix is singular and the
*>                solutions X have not been computed.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup complexOTHERcomputational
*
*  =====================================================================
      SUBROUTINE ctptrs( UPLO, TRANS, DIAG, N, NRHS, AP, B, LDB, INFO )
*
*  -- LAPACK computational routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      CHARACTER          DIAG, TRANS, UPLO
      INTEGER            INFO, LDB, N, NRHS
*     ..
*     .. Array Arguments ..
      COMPLEX            AP( * ), B( LDB, * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      COMPLEX            ZERO
      parameter( zero = ( 0.0e+0, 0.0e+0 ) )
*     ..
*     .. Local Scalars ..
      LOGICAL            NOUNIT, UPPER
      INTEGER            J, JC
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           lsame
*     ..
*     .. External Subroutines ..
      EXTERNAL           ctpsv, xerbla
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          max
*     ..
*     .. 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
.NOT.      ELSE IF( LSAME( TRANS, 'n.AND..NOT.' )  
     $         LSAME( TRANS, 't.AND..NOT.' )  LSAME( TRANS, 'c' ) ) THEN
         INFO = -2
.NOT..AND..NOT.      ELSE IF( NOUNIT  LSAME( DIAG, 'u' ) ) THEN
         INFO = -3
.LT.      ELSE IF( N0 ) THEN
         INFO = -4
.LT.      ELSE IF( NRHS0 ) THEN
         INFO = -5
.LT.      ELSE IF( LDBMAX( 1, N ) ) THEN
         INFO = -8
      END IF
.NE.      IF( INFO0 ) THEN
         CALL XERBLA( 'ctptrs', -INFO )
         RETURN
      END IF
*
*     Quick return if possible
*
.EQ.      IF( N0 )
     $   RETURN
*
*     Check for singularity.
*
      IF( NOUNIT ) THEN
         IF( UPPER ) THEN
            JC = 1
            DO 10 INFO = 1, N
.EQ.               IF( AP( JC+INFO-1 )ZERO )
     $            RETURN
               JC = JC + INFO
   10       CONTINUE
         ELSE
            JC = 1
            DO 20 INFO = 1, N
.EQ.               IF( AP( JC )ZERO )
     $            RETURN
               JC = JC + N - INFO + 1
   20       CONTINUE
         END IF
      END IF
      INFO = 0
*
*     Solve  A * x = b,  A**T * x = b,  or  A**H * x = b.
*
      DO 30 J = 1, NRHS
         CALL CTPSV( UPLO, TRANS, DIAG, N, AP, B( 1, J ), 1 )
   30 CONTINUE
*
      RETURN
*
*     End of CTPTRS
*
      END