Product of a Scalar and Vector Plus a Vector

Calling Sequence

CALL DAXPY	(N, DALPHA, DX, INCX, DY, INCY)
CALL SAXPY	(N, SALPHA, SX, INCX, SY, INCY)
CALL ZAXPY	(N, ZALPHA, ZX, INCX, ZY, INCY)
CALL CAXPY	(N, CALPHA, CX, INCX, CY, INCY)
void daxpy	(int n, double da, double *dx, int incx, double *dy, (int incy)
void saxpy	(int n, float sa, float *sx, int incx, float *sy, int incy)
void zaxpy	(int n, doublecomplex *za, doublecomplex *zx, int incx, doublecomplex *zy, int incy)
void caxpy	(int n, complex *ca, complex *cx, int incx, complex *cy, int incy)

Arguments

N	Number of elements in the vector. N 0.
xALPHA	Scalar that will be applied to vector X.
xX	Input vector X; the size of array X must be at least max(1,N*|INCX|).
INCX	Specifies the storage spacing between successive elements of the vector X. A value of one indicates that the elements of the vector are consecutive in memory.
	If X refers to a two-dimensional array and the value of INCX is equal to the leading dimension of X then the elements of the vector will be a row of X.
	If X refers to a two-dimensional array and the value of INCX is equal to the leading dimension of X plus one then the elements of the vector will be a diagonal of X.
xY	Result vector Y; the size of array Y must be at least max(1,N*|INCY|).
INCY	Specifies the storage spacing between successive elements of the vector Y. A value of one indicates that the elements of the vector are consecutive in memory.
	If Y refers to a two-dimensional array and the value of INCY is equal to the leading dimension of Y then the elements of the vector will be a row of Y.
	If Y refers to a two-dimensional array and the value of INCY is equal to the leading dimension of Y plus one then the elements of the vector will be a diagonal of Y.

Sample Program

PROGRAM TEST

IMPLICIT NONE

C

INTEGER N

PARAMETER (N = 3)

C

INTEGER ICOL, INCX, INCY, IROW

DOUBLE PRECISION SCALE, X(N,N)

C

EXTERNAL DAXPY

C

C Initialize the array X to contain the matrix X shown below.

C

C 5.0 4.0 3.0

C X = 2.5 3.0 3.5

C 1.0 1.5 2.0

C

DATA X / 5.0D0, 2.5D0, 1.0D0, 4.0D0, 3.0D0, 1.5D0,

$ 3.0D0, 3.5D0, 2.0D0 /

C

PRINT 1000

PRINT 1010, ((X(IROW,ICOL), ICOL = 1, N), IROW = 1, N)

INCX = N

INCY = N

SCALE = - X(2,1) / X(1,1)

CALL DAXPY (N, SCALE, X(1,1), INCX, X(2,1), INCY)

PRINT 1020

PRINT 1010, ((X(IROW,ICOL), ICOL = 1, N), IROW = 1, N)

C

1000 FORMAT (1X, 'X:')

1010 FORMAT (3(2X, F4.2))

1020 FORMAT (/1X, 'After one elimination:')

C

END

Sample Output

X:
5.00 4.00 3.00
2.50 3.00 3.50
1.00 1.50 2.00
After one elimination:
5.00 4.00 3.00
0.00 1.00 2.00
1.00 1.50 2.00