dtrttp.f

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*> \brief \b DTRTTP copies a triangular matrix from the standard full format (TR) to the standard packed format (TP).
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
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*> [TXT]</a>
*
*  Definition:
*  ===========
*
*       SUBROUTINE DTRTTP( UPLO, N, A, LDA, AP, INFO )
*
*       .. Scalar Arguments ..
*       CHARACTER          UPLO
*       INTEGER            INFO, N, LDA
*       ..
*       .. Array Arguments ..
*       DOUBLE PRECISION   A( LDA, * ), AP( * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> DTRTTP copies a triangular matrix A from full format (TR) to standard
*> packed format (TP).
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] UPLO
*> \verbatim
*>          UPLO is CHARACTER*1
*>          = 'U':  A is upper triangular.
*>          = 'L':  A is lower triangular.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The order of the matrices AP and A.  N >= 0.
*> \endverbatim
*>
*> \param[in] A
*> \verbatim
*>          A is DOUBLE PRECISION array, dimension (LDA,N)
*>          On exit, the triangular matrix A.  If UPLO = 'U', the leading
*>          N-by-N upper triangular part of A contains the upper
*>          triangular part of the matrix A, and the strictly lower
*>          triangular part of A is not referenced.  If UPLO = 'L', the
*>          leading N-by-N lower triangular part of A contains the lower
*>          triangular part of the matrix A, and the strictly upper
*>          triangular part of A is not referenced.
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*>          LDA is INTEGER
*>          The leading dimension of the array A.  LDA >= max(1,N).
*> \endverbatim
*>
*> \param[out] AP
*> \verbatim
*>          AP is DOUBLE PRECISION array, dimension (N*(N+1)/2)
*>          On exit, 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)*(2n-j)/2) = A(i,j) for j<=i<=n.
*> \endverbatim
*>
*> \param[out] INFO
*> \verbatim
*>          INFO is INTEGER
*>          = 0:  successful exit
*>          < 0:  if INFO = -i, the i-th argument had an illegal value
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup trttp
*
*  =====================================================================
      SUBROUTINE dtrttp( UPLO, N, A, LDA, AP, 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          UPLO
      INTEGER            INFO, N, LDA
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION   A( LDA, * ), AP( * )
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
*     ..
*     .. Local Scalars ..
      LOGICAL            LOWER
      INTEGER            I, J, K
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           lsame
*     ..
*     .. External Subroutines ..
      EXTERNAL           xerbla
*     ..
*     .. Executable Statements ..
*
*     Test the input parameters.
*
      info = 0
      lower = lsame( uplo, 'L' )
      IF( .NOT.lower .AND. .NOT.lsame( uplo, 'U' ) ) 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( 'DTRTTP', -info )
         RETURN
      END IF
*
      IF( lower ) THEN
         k = 0
         DO j = 1, n
            DO i = j, n
               k = k + 1
               ap( k ) = a( i, j )
            END DO
         END DO
      ELSE
         k = 0
         DO j = 1, n
            DO i = 1, j
               k = k + 1
               ap( k ) = a( i, j )
            END DO
         END DO
      END IF
*
*
      RETURN
*
*     End of DTRTTP
*
      END