NAG Library Function Document

nag_daxpby (f16ecc)

+− Contents

1 Purpose

9 Example

nag_daxpby (f16ecc) performs the operation

y \leftarrow α x + β y .

#include <nag.h>

#include <nagf16.h>

void	nag_daxpby (Integer n, double alpha, const double x[], Integer incx, double beta, double y[], Integer incy, NagError *fail)

nag_daxpby (f16ecc) performs the operation

y \leftarrow α x + β y

where

x

and

y

are

n

-element real vectors, and

α

and

β

real scalars. If

n

is equal to zero, or if

α

is equal to zero and

β

is equal to one, this function returns immediately.

The BLAS Technical Forum Standard (2001) http://www.netlib.org/blas/blast-forum

1: n – IntegerInput: On entry: $n$ , the number of elements in $x$ and $y$ .
Constraint: $n \geq 0$ .
2: alpha – doubleInput: On entry: the scalar $α$ .
3: x[ $\dim$ ] – const doubleInput: Note: the dimension, dim, of the array x must be at least $\max (1, 1 + (n - 1) |incx|)$ .
On entry: the vector $x$ .
4: incx – IntegerInput: On entry: the increment in the subscripts of x between successive elements of $x$ .
Constraint: $incx \neq 0$ .
5: beta – doubleInput: On entry: the scalar $β$ .
6: y[ $\dim$ ] – doubleInput/Output: Note: the dimension, dim, of the array y must be at least $\max (1, 1 + (n - 1) |incy|)$ .
On entry: the vector $y$ .

On exit: the updated vector $y$ .
7: incy – IntegerInput: On entry: the increment in the subscripts of y between successive elements of $y$ .
Constraint: $incy \neq 0$ .
8: fail – NagError *Input/Output: The NAG error argument (see Section 3.6 in the Essential Introduction).

NE_BAD_PARAM: On entry, argument $〈value〉$ had an illegal value.
NE_INT: On entry, $incx = 〈value〉$ .
Constraint: $incx \neq 0$ .; On entry, $incy = 〈value〉$ .
Constraint: $incy \neq 0$ .; On entry, $n = 〈value〉$ .
Constraint: $n \geq 0$ .

The BLAS standard requires accurate implementations which avoid unnecessary over/underflow (see Section 2.7 of The BLAS Technical Forum Standard (2001)).