f16 Chapter Contents
f16 Chapter Introduction
NAG C Library Manual

# NAG Library Function Documentnag_daxpby (f16ecc)

## 1  Purpose

nag_daxpby (f16ecc) performs the operation
 $y←αx+β y .$

## 2  Specification

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

## 3  Description

nag_daxpby (f16ecc) performs the operation
 $y←α x+β y$
where $x$ and $y$ are $n$-element real vectors, and $\alpha$ and $\beta$ real scalars. If $n$ is equal to zero, or if $\alpha$ is equal to zero and $\beta$ is equal to one, this function returns immediately.

## 4  References

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

## 5  Arguments

1:     nIntegerInput
On entry: $n$, the number of elements in $x$ and $y$.
Constraint: ${\mathbf{n}}\ge 0$.
On entry: the scalar $\alpha$.
3:     x[$\mathit{dim}$]const doubleInput
Note: the dimension, dim, of the array x must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,1+\left({\mathbf{n}}-1\right)\left|{\mathbf{incx}}\right|\right)$.
On entry: the vector $x$.
4:     incxIntegerInput
On entry: the increment in the subscripts of x between successive elements of $x$.
Constraint: ${\mathbf{incx}}\ne 0$.
On entry: the scalar $\beta$.
6:     y[$\mathit{dim}$]doubleInput/Output
Note: the dimension, dim, of the array y must be at least $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,1+\left({\mathbf{n}}-1\right)\left|{\mathbf{incy}}\right|\right)$.
On entry: the vector $y$.
On exit: the updated vector $y$.
7:     incyIntegerInput
On entry: the increment in the subscripts of y between successive elements of $y$.
Constraint: ${\mathbf{incy}}\ne 0$.
8:     failNagError *Input/Output
The NAG error argument (see Section 3.6 in the Essential Introduction).

## 6  Error Indicators and Warnings

On entry, argument $〈\mathit{\text{value}}〉$ had an illegal value.
NE_INT
On entry, ${\mathbf{incx}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{incx}}\ne 0$.
On entry, ${\mathbf{incy}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{incy}}\ne 0$.
On entry, ${\mathbf{n}}=〈\mathit{\text{value}}〉$.
Constraint: ${\mathbf{n}}\ge 0$.

## 7  Accuracy

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