slaset.f

Go to the documentation of this file.

*> \brief \b SLASET initializes the off-diagonal elements and the diagonal elements of a matrix to given values.
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*> \htmlonly
*> Download SLASET + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slaset.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/slaset.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slaset.f">
*> [TXT]</a>
*> \endhtmlonly
*
*  Definition:
*  ===========
*
*       SUBROUTINE SLASET( UPLO, M, N, ALPHA, BETA, A, LDA )
*
*       .. Scalar Arguments ..
*       CHARACTER          UPLO
*       INTEGER            LDA, M, N
*       REAL               ALPHA, BETA
*       ..
*       .. Array Arguments ..
*       REAL               A( LDA, * )
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> SLASET initializes an m-by-n matrix A to BETA on the diagonal and
*> ALPHA on the offdiagonals.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] UPLO
*> \verbatim
*>          UPLO is CHARACTER*1
*>          Specifies the part of the matrix A to be set.
*>          = 'U':      Upper triangular part is set; the strictly lower
*>                      triangular part of A is not changed.
*>          = 'L':      Lower triangular part is set; the strictly upper
*>                      triangular part of A is not changed.
*>          Otherwise:  All of the matrix A is set.
*> \endverbatim
*>
*> \param[in] M
*> \verbatim
*>          M is INTEGER
*>          The number of rows of the matrix A.  M >= 0.
*> \endverbatim
*>
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>          The number of columns of the matrix A.  N >= 0.
*> \endverbatim
*>
*> \param[in] ALPHA
*> \verbatim
*>          ALPHA is REAL
*>          The constant to which the offdiagonal elements are to be set.
*> \endverbatim
*>
*> \param[in] BETA
*> \verbatim
*>          BETA is REAL
*>          The constant to which the diagonal elements are to be set.
*> \endverbatim
*>
*> \param[out] A
*> \verbatim
*>          A is REAL array, dimension (LDA,N)
*>          On exit, the leading m-by-n submatrix of A is set as follows:
*>
*>          if UPLO = 'U', A(i,j) = ALPHA, 1<=i<=j-1, 1<=j<=n,
*>          if UPLO = 'L', A(i,j) = ALPHA, j+1<=i<=m, 1<=j<=n,
*>          otherwise,     A(i,j) = ALPHA, 1<=i<=m, 1<=j<=n, i.ne.j,
*>
*>          and, for all UPLO, A(i,i) = BETA, 1<=i<=min(m,n).
*> \endverbatim
*>
*> \param[in] LDA
*> \verbatim
*>          LDA is INTEGER
*>          The leading dimension of the array A.  LDA >= max(1,M).
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup laset
*
*  =====================================================================
      SUBROUTINE slaset( UPLO, M, N, ALPHA, BETA, A, LDA )
*
*  -- LAPACK auxiliary 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            LDA, M, N
      REAL               ALPHA, BETA
*     ..
*     .. Array Arguments ..
      REAL               A( LDA, * )
*     ..
*
* =====================================================================
*
*     .. Local Scalars ..
      INTEGER            I, J
*     ..
*     .. External Functions ..
      LOGICAL            LSAME
      EXTERNAL           lsame
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          min
*     ..
*     .. Executable Statements ..
*
      IF( lsame( uplo, 'U' ) ) THEN
*
*        Set the strictly upper triangular or trapezoidal part of the
*        array to ALPHA.
*
         DO 20 j = 2, n
            DO 10 i = 1, min( j-1, m )
               a( i, j ) = alpha
   10       CONTINUE
   20    CONTINUE
*
      ELSE IF( lsame( uplo, 'L' ) ) THEN
*
*        Set the strictly lower triangular or trapezoidal part of the
*        array to ALPHA.
*
         DO 40 j = 1, min( m, n )
            DO 30 i = j + 1, m
               a( i, j ) = alpha
   30       CONTINUE
   40    CONTINUE
*
      ELSE
*
*        Set the leading m-by-n submatrix to ALPHA.
*
         DO 60 j = 1, n
            DO 50 i = 1, m
               a( i, j ) = alpha
   50       CONTINUE
   60    CONTINUE
      END IF
*
*     Set the first min(M,N) diagonal elements to BETA.
*
      DO 70 i = 1, min( m, n )
         a( i, i ) = beta
   70 CONTINUE
*
      RETURN
*
*     End of SLASET
*
      END