slaset.f

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      SUBROUTINE slaset( UPLO, M, N, ALPHA, BETA, A, LDA )
*
*  -- LAPACK auxiliary routine (version 3.2) --
*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
*     November 2006
*
*     .. Scalar Arguments ..
      CHARACTER          uplo
      INTEGER            lda, m, n
      REAL               alpha, beta
*     ..
*     .. Array Arguments ..
      REAL               a( lda, * )
*     ..
*
*  Purpose
*  =======
*
*  SLASET initializes an m-by-n matrix A to BETA on the diagonal and
*  ALPHA on the offdiagonals.
*
*  Arguments
*  =========
*
*  UPLO    (input) 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.
*
*  M       (input) INTEGER
*          The number of rows of the matrix A.  M >= 0.
*
*  N       (input) INTEGER
*          The number of columns of the matrix A.  N >= 0.
*
*  ALPHA   (input) REAL
*          The constant to which the offdiagonal elements are to be set.
*
*  BETA    (input) REAL
*          The constant to which the diagonal elements are to be set.
*
*  A       (input/output) 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).
*
*  LDA     (input) INTEGER
*          The leading dimension of the array A.  LDA >= max(1,M).
*
* =====================================================================
*
*     .. 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