Source module last modified on Thu, 2 Jul 1998, 23:17;
HTML image of Fortran source automatically generated by
for2html on Sun, 23 Jun 2002, 15:10.
SUBROUTINE DGEMV ( TRANS, M, N, ALPHA, A, LDA, X, INCX,
$ BETA, Y, INCY )
# .. Scalar Arguments ..
DOUBLE PRECISION ALPHA, BETA
INTEGER INCX, INCY, LDA, M, N
CHARACTER*1 TRANS
# .. Array Arguments ..
DOUBLE PRECISION A( LDA, * ), X( * ), Y( * )
# ..
#
# Purpose
# =======
#
# DGEMV performs one of the matrix-vector operations
#
# y := alpha*A*x + beta*y, or y := alpha*A'*x + beta*y,
#
# where alpha and beta are scalars, x and y are vectors and A is an
# m by n matrix.
#
# Parameters
# ==========
#
# TRANS - CHARACTER*1.
# On entry, TRANS specifies the operation to be performed as
# follows:
#
# TRANS = 'N' or 'n' y := alpha*A*x + beta*y.
#
# TRANS = 'T' or 't' y := alpha*A'*x + beta*y.
#
# TRANS = 'C' or 'c' y := alpha*A'*x + beta*y.
#
# Unchanged on exit.
#
# M - INTEGER.
# On entry, M specifies the number of rows of the matrix A.
# M must be at least zero.
# Unchanged on exit.
#
# N - INTEGER.
# On entry, N specifies the number of columns of the matrix A.
# N must be at least zero.
# Unchanged on exit.
#
# ALPHA - DOUBLE PRECISION.
# On entry, ALPHA specifies the scalar alpha.
# Unchanged on exit.
#
# A - DOUBLE PRECISION array of DIMENSION ( LDA, n ).
# Before entry, the leading m by n part of the array A must
# contain the matrix of coefficients.
# Unchanged on exit.
#
# LDA - 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 ).
# Unchanged on exit.
#
# X - DOUBLE PRECISION array of DIMENSION at least
# ( 1 + ( n - 1 )*abs( INCX ) ) when TRANS = 'N' or 'n'
# and at least
# ( 1 + ( m - 1 )*abs( INCX ) ) otherwise.
# Before entry, the incremented array X must contain the
# vector x.
# Unchanged on exit.
#
# INCX - INTEGER.
# On entry, INCX specifies the increment for the elements of
# X. INCX must not be zero.
# Unchanged on exit.
#
# BETA - DOUBLE PRECISION.
# On entry, BETA specifies the scalar beta. When BETA is
# supplied as zero then Y need not be set on input.
# Unchanged on exit.
#
# Y - DOUBLE PRECISION array of DIMENSION at least
# ( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n'
# and at least
# ( 1 + ( n - 1 )*abs( INCY ) ) otherwise.
# Before entry with BETA non-zero, the incremented array Y
# must contain the vector y. On exit, Y is overwritten by the
# updated vector y.
#
# INCY - INTEGER.
# On entry, INCY specifies the increment for the elements of
# Y. INCY must not be zero.
# Unchanged on exit.
#
#
# 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.
#
#
# .. Parameters ..
DOUBLE PRECISION ONE , ZERO
PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
# .. Local Scalars ..
DOUBLE PRECISION TEMP
INTEGER I, INFO, IX, IY, J, JX, JY, KX, KY, LENX, LENY
# .. External Functions ..
LOGICAL LSAME
EXTERNAL LSAME
# .. External Subroutines ..
EXTERNAL XERBLA
# .. Intrinsic Functions ..
INTRINSIC MAX
# ..
# .. Executable Statements ..
#
# Test the input parameters.
#
INFO = 0
IF ( ! LSAME( TRANS, 'N' )&&
$ ! LSAME( TRANS, 'T' )&&
$ ! LSAME( TRANS, 'C' ) )THEN
INFO = 1
ELSE IF( M<0 )THEN
INFO = 2
ELSE IF( N<0 )THEN
INFO = 3
ELSE IF( LDA<MAX( 1, M ) )THEN
INFO = 6
ELSE IF( INCX==0 )THEN
INFO = 8
ELSE IF( INCY==0 )THEN
INFO = 11
END IF
IF( INFO!=0 )THEN
CALL XERBLA( 'DGEMV ', INFO )
RETURN
END IF
#
# Quick return if possible.
#
IF( ( M==0 )||( N==0 )||
$ ( ( ALPHA==ZERO )&&( BETA==ONE ) ) )
$ RETURN
#
# Set LENX and LENY, the lengths of the vectors x and y, and set
# up the start points in X and Y.
#
IF( LSAME( TRANS, 'N' ) )THEN
LENX = N
LENY = M
ELSE
LENX = M
LENY = N
END IF
IF( INCX>0 )THEN
KX = 1
ELSE
KX = 1 - ( LENX - 1 )*INCX
END IF
IF( INCY>0 )THEN
KY = 1
ELSE
KY = 1 - ( LENY - 1 )*INCY
END IF
#
# Start the operations. In this version the elements of A are
# accessed sequentially with one pass through A.
#
# First form y := beta*y.
#
IF( BETA!=ONE )THEN
IF( INCY==1 )THEN
IF( BETA==ZERO )THEN
DO 10, I = 1, LENY
Y( I ) = ZERO
10 CONTINUE
ELSE
DO 20, I = 1, LENY
Y( I ) = BETA*Y( I )
20 CONTINUE
END IF
ELSE
IY = KY
IF( BETA==ZERO )THEN
DO 30, I = 1, LENY
Y( IY ) = ZERO
IY = IY + INCY
30 CONTINUE
ELSE
DO 40, I = 1, LENY
Y( IY ) = BETA*Y( IY )
IY = IY + INCY
40 CONTINUE
END IF
END IF
END IF
IF( ALPHA==ZERO )
$ RETURN
IF( LSAME( TRANS, 'N' ) )THEN
#
# Form y := alpha*A*x + y.
#
JX = KX
IF( INCY==1 )THEN
DO 60, J = 1, N
IF( X( JX )!=ZERO )THEN
TEMP = ALPHA*X( JX )
DO 50, I = 1, M
Y( I ) = Y( I ) + TEMP*A( I, J )
50 CONTINUE
END IF
JX = JX + INCX
60 CONTINUE
ELSE
DO 80, J = 1, N
IF( X( JX )!=ZERO )THEN
TEMP = ALPHA*X( JX )
IY = KY
DO 70, I = 1, M
Y( IY ) = Y( IY ) + TEMP*A( I, J )
IY = IY + INCY
70 CONTINUE
END IF
JX = JX + INCX
80 CONTINUE
END IF
ELSE
#
# Form y := alpha*A'*x + y.
#
JY = KY
IF( INCX==1 )THEN
DO 100, J = 1, N
TEMP = ZERO
DO 90, I = 1, M
TEMP = TEMP + A( I, J )*X( I )
90 CONTINUE
Y( JY ) = Y( JY ) + ALPHA*TEMP
JY = JY + INCY
100 CONTINUE
ELSE
DO 120, J = 1, N
TEMP = ZERO
IX = KX
DO 110, I = 1, M
TEMP = TEMP + A( I, J )*X( IX )
IX = IX + INCX
110 CONTINUE
Y( JY ) = Y( JY ) + ALPHA*TEMP
JY = JY + INCY
120 CONTINUE
END IF
END IF
#
RETURN
#
# End of DGEMV .
#
END