slaset.f

          SUBROUTINE SLASET( UPLO, M, N, ALPHA, BETA, A, LDA )
    *
    *  -- LAPACK auxiliary routine (version 3.1) --
    *     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