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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