dgemvf.f

SUBROUTINEDGEMVF ( 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 ..
* .. Intrinsic Functions ..
INTRINSIC MAX
* ..
* .. Executable Statements ..
*
* Test the input parameters.
*
 INFO =0
IF ( .NOT.LSAME( TRANS, 'N' ).AND.
 $ .NOT.LSAME( TRANS, 'T' ).AND.
 $ .NOT.LSAME( TRANS, 'C' ) )THEN
 INFO =1
ELSEIF( M.LT.0 )THEN
 INFO =2
ELSEIF( N.LT.0 )THEN
 INFO =3
ELSEIF( LDA.LT.MAX( 1, M ) )THEN
 INFO =6
ELSEIF( INCX.EQ.0 )THEN
 INFO =8
ELSEIF( INCY.EQ.0 )THEN
 INFO =11
END IF
*
* Quick return if possible.
*
IF( ( M.EQ.0 ).OR.( N.EQ.0 ).OR.
 $ ( ( ALPHA.EQ.ZERO ).AND.( BETA.EQ.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.GT.0 )THEN
 KX =1
ELSE
 KX =1- ( LENX -1 )*INCX
END IF
IF( INCY.GT.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.NE.ONE )THEN
IF( INCY.EQ.1 )THEN
IF( BETA.EQ.ZERO )THEN
DO10, I =1, LENY
 Y( I ) = ZERO
10CONTINUE
ELSE
DO20, I =1, LENY
 Y( I ) = BETA*Y( I )
20CONTINUE
END IF
ELSE
 IY = KY
IF( BETA.EQ.ZERO )THEN
DO30, I =1, LENY
 Y( IY ) = ZERO
 IY = IY + INCY
30CONTINUE
ELSE
DO40, I =1, LENY
 Y( IY ) = BETA*Y( IY )
 IY = IY + INCY
40CONTINUE
END IF
END IF
END IF
IF( ALPHA.EQ.ZERO )
 $ RETURN
IF( LSAME( TRANS, 'N' ) )THEN
*
* Form y := alpha*A*x + y.
*
 JX = KX
IF( INCY.EQ.1 )THEN
DO60, J =1, N
IF( X( JX ).NE.ZERO )THEN
 TEMP = ALPHA*X( JX )
DO50, I =1, M
 Y( I ) = Y( I ) + TEMP*A( I, J )
50CONTINUE
END IF
 JX = JX + INCX
60CONTINUE
ELSE
DO80, J =1, N
IF( X( JX ).NE.ZERO )THEN
 TEMP = ALPHA*X( JX )
 IY = KY
DO70, I =1, M
 Y( IY ) = Y( IY ) + TEMP*A( I, J )
 IY = IY + INCY
70CONTINUE
END IF
 JX = JX + INCX
80CONTINUE
END IF
ELSE
*
* Form y := alpha*A'*x + y.
*
 JY = KY
IF( INCX.EQ.1 )THEN
DO100, J =1, N
 TEMP = ZERO
DO90, I =1, M
 TEMP = TEMP + A( I, J )*X( I )
90CONTINUE
 Y( JY ) = Y( JY ) + ALPHA*TEMP
 JY = JY + INCY
100CONTINUE
ELSE
DO120, J =1, N
 TEMP = ZERO
 IX = KX
DO110, I =1, M
 TEMP = TEMP + A( I, J )*X( IX )
 IX = IX + INCX
110CONTINUE
 Y( JY ) = Y( JY ) + ALPHA*TEMP
 JY = JY + INCY
120CONTINUE
END IF
END IF
*
RETURN
*
* End of DGEMV .
*
END