forked from lijiext/lammps
163 lines
4.3 KiB
Fortran
163 lines
4.3 KiB
Fortran
SUBROUTINE DGER(M,N,ALPHA,X,INCX,Y,INCY,A,LDA)
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* .. Scalar Arguments ..
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DOUBLE PRECISION ALPHA
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INTEGER INCX,INCY,LDA,M,N
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* ..
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* .. Array Arguments ..
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DOUBLE PRECISION A(LDA,*),X(*),Y(*)
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* ..
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*
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* Purpose
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* =======
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*
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* DGER performs the rank 1 operation
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*
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* A := alpha*x*y' + A,
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*
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* where alpha is a scalar, x is an m element vector, y is an n element
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* vector and A is an m by n matrix.
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*
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* Arguments
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* ==========
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*
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* M - INTEGER.
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* On entry, M specifies the number of rows of the matrix A.
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* M must be at least zero.
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* Unchanged on exit.
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*
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* N - INTEGER.
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* On entry, N specifies the number of columns of the matrix A.
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* N must be at least zero.
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* Unchanged on exit.
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*
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* ALPHA - DOUBLE PRECISION.
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* On entry, ALPHA specifies the scalar alpha.
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* Unchanged on exit.
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*
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* X - DOUBLE PRECISION array of dimension at least
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* ( 1 + ( m - 1 )*abs( INCX ) ).
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* Before entry, the incremented array X must contain the m
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* element vector x.
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* Unchanged on exit.
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*
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* INCX - INTEGER.
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* On entry, INCX specifies the increment for the elements of
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* X. INCX must not be zero.
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* Unchanged on exit.
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*
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* Y - DOUBLE PRECISION array of dimension at least
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* ( 1 + ( n - 1 )*abs( INCY ) ).
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* Before entry, the incremented array Y must contain the n
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* element vector y.
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* Unchanged on exit.
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*
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* INCY - INTEGER.
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* On entry, INCY specifies the increment for the elements of
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* Y. INCY must not be zero.
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* Unchanged on exit.
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*
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* A - DOUBLE PRECISION array of DIMENSION ( LDA, n ).
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* Before entry, the leading m by n part of the array A must
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* contain the matrix of coefficients. On exit, A is
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* overwritten by the updated matrix.
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*
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* LDA - INTEGER.
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* On entry, LDA specifies the first dimension of A as declared
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* in the calling (sub) program. LDA must be at least
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* max( 1, m ).
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* Unchanged on exit.
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*
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* Further Details
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* ===============
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*
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* Level 2 Blas routine.
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*
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* -- Written on 22-October-1986.
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* Jack Dongarra, Argonne National Lab.
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* Jeremy Du Croz, Nag Central Office.
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* Sven Hammarling, Nag Central Office.
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* Richard Hanson, Sandia National Labs.
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*
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* =====================================================================
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*
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* .. Parameters ..
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DOUBLE PRECISION ZERO
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PARAMETER (ZERO=0.0D+0)
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* ..
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* .. Local Scalars ..
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DOUBLE PRECISION TEMP
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INTEGER I,INFO,IX,J,JY,KX
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* ..
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* .. External Subroutines ..
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EXTERNAL XERBLA
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* ..
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* .. Intrinsic Functions ..
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INTRINSIC MAX
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* ..
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*
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* Test the input parameters.
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*
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INFO = 0
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IF (M.LT.0) THEN
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INFO = 1
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ELSE IF (N.LT.0) THEN
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INFO = 2
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ELSE IF (INCX.EQ.0) THEN
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INFO = 5
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ELSE IF (INCY.EQ.0) THEN
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INFO = 7
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ELSE IF (LDA.LT.MAX(1,M)) THEN
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INFO = 9
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END IF
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IF (INFO.NE.0) THEN
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CALL XERBLA('DGER ',INFO)
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RETURN
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END IF
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*
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* Quick return if possible.
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*
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IF ((M.EQ.0) .OR. (N.EQ.0) .OR. (ALPHA.EQ.ZERO)) RETURN
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*
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* Start the operations. In this version the elements of A are
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* accessed sequentially with one pass through A.
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*
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IF (INCY.GT.0) THEN
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JY = 1
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ELSE
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JY = 1 - (N-1)*INCY
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END IF
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IF (INCX.EQ.1) THEN
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DO 20 J = 1,N
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IF (Y(JY).NE.ZERO) THEN
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TEMP = ALPHA*Y(JY)
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DO 10 I = 1,M
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A(I,J) = A(I,J) + X(I)*TEMP
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10 CONTINUE
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END IF
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JY = JY + INCY
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20 CONTINUE
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ELSE
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IF (INCX.GT.0) THEN
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KX = 1
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ELSE
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KX = 1 - (M-1)*INCX
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END IF
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DO 40 J = 1,N
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IF (Y(JY).NE.ZERO) THEN
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TEMP = ALPHA*Y(JY)
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IX = KX
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DO 30 I = 1,M
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A(I,J) = A(I,J) + X(IX)*TEMP
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IX = IX + INCX
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30 CONTINUE
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END IF
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JY = JY + INCY
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40 CONTINUE
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END IF
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*
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RETURN
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*
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* End of DGER .
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*
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END
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