dger()

subroutine dger	(	integer	m,
		integer	n,
		double precision	alpha,
		double precision, dimension(*)	x,
		integer	incx,
		double precision, dimension(*)	y,
		integer	incy,
		double precision, dimension(lda,*)	a,
		integer	lda )

DGER

Purpose:

!>
!> DGER   performs the rank 1 operation
!>
!>    A := alpha*x*y**T + A,
!>
!> where alpha is a scalar, x is an m element vector, y is an n element
!> vector and A is an m by n matrix.
!> 

Parameters

[in]	M	!> M is INTEGER !> On entry, M specifies the number of rows of the matrix A. !> M must be at least zero. !>
[in]	N	!> N is INTEGER !> On entry, N specifies the number of columns of the matrix A. !> N must be at least zero. !>
[in]	ALPHA	!> ALPHA is DOUBLE PRECISION. !> On entry, ALPHA specifies the scalar alpha. !>
[in]	X	!> X is DOUBLE PRECISION array, dimension at least !> ( 1 + ( m - 1 )*abs( INCX ) ). !> Before entry, the incremented array X must contain the m !> element vector x. !>
[in]	INCX	!> INCX is INTEGER !> On entry, INCX specifies the increment for the elements of !> X. INCX must not be zero. !>
[in]	Y	!> Y is DOUBLE PRECISION array, dimension at least !> ( 1 + ( n - 1 )*abs( INCY ) ). !> Before entry, the incremented array Y must contain the n !> element vector y. !>
[in]	INCY	!> INCY is INTEGER !> On entry, INCY specifies the increment for the elements of !> Y. INCY must not be zero. !>
[in,out]	A	!> A is DOUBLE PRECISION array, dimension ( LDA, N ) !> Before entry, the leading m by n part of the array A must !> contain the matrix of coefficients. On exit, A is !> overwritten by the updated matrix. !>
[in]	LDA	!> LDA is INTEGER !> On entry, LDA specifies the first dimension of A as declared !> in the calling (sub) program. LDA must be at least !> max( 1, m ). !>

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Further Details:

!>
!>  Level 2 Blas routine.
!>
!>  -- Written on 22-October-1986.
!>     Jack Dongarra, Argonne National Lab.
!>     Jeremy Du Croz, Nag Central Office.
!>     Sven Hammarling, Nag Central Office.
!>     Richard Hanson, Sandia National Labs.
!> 

Definition at line 129 of file dger.f.

*
*  -- Reference BLAS level2 routine --
*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      DOUBLE PRECISION ALPHA
      INTEGER INCX,INCY,LDA,M,N
*     ..
*     .. Array Arguments ..
      DOUBLE PRECISION A(LDA,*),X(*),Y(*)
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION ZERO
      parameter(zero=0.0d+0)
*     ..
*     .. Local Scalars ..
      DOUBLE PRECISION TEMP
      INTEGER I,INFO,IX,J,JY,KX
*     ..
*     .. External Subroutines ..
      EXTERNAL xerbla
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC max
*     ..
*
*     Test the input parameters.
*
      info = 0
      IF (m.LT.0) THEN
          info = 1
      ELSE IF (n.LT.0) THEN
          info = 2
      ELSE IF (incx.EQ.0) THEN
          info = 5
      ELSE IF (incy.EQ.0) THEN
          info = 7
      ELSE IF (lda.LT.max(1,m)) THEN
          info = 9
      END IF
      IF (info.NE.0) THEN
          CALL xerbla('DGER  ',info)
          RETURN
      END IF
*
*     Quick return if possible.
*
      IF ((m.EQ.0) .OR. (n.EQ.0) .OR. (alpha.EQ.zero)) RETURN
*
*     Start the operations. In this version the elements of A are
*     accessed sequentially with one pass through A.
*
      IF (incy.GT.0) THEN
          jy = 1
      ELSE
          jy = 1 - (n-1)*incy
      END IF
      IF (incx.EQ.1) THEN
          DO 20 j = 1,n
              IF (y(jy).NE.zero) THEN
                  temp = alpha*y(jy)
                  DO 10 i = 1,m
                      a(i,j) = a(i,j) + x(i)*temp
   10             CONTINUE
              END IF
              jy = jy + incy
   20     CONTINUE
      ELSE
          IF (incx.GT.0) THEN
              kx = 1
          ELSE
              kx = 1 - (m-1)*incx
          END IF
          DO 40 j = 1,n
              IF (y(jy).NE.zero) THEN
                  temp = alpha*y(jy)
                  ix = kx
                  DO 30 i = 1,m
                      a(i,j) = a(i,j) + x(ix)*temp
                      ix = ix + incx
   30             CONTINUE
              END IF
              jy = jy + incy
   40     CONTINUE
      END IF
*
      RETURN
*
*     End of DGER
*

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