nag_dwaxpby (f16ehc) (PDF version)
f16 Chapter Contents
f16 Chapter Introduction
NAG Library Manual

NAG Library Function Document

nag_dwaxpby (f16ehc)

 Contents

    1  Purpose
    7  Accuracy

1  Purpose

nag_dwaxpby (f16ehc) computes the sum of two scaled vectors, preserving input, for real scalars and vectors.

2  Specification

#include <nag.h>
#include <nagf16.h>
void  nag_dwaxpby (Integer n, double alpha, const double x[], Integer incx, double beta, const double y[], Integer incy, double w[], Integer incw, NagError *fail)

3  Description

nag_dwaxpby (f16ehc) performs the operation
w αx+βy,  
where x and y are n-element real vectors, and α and β are real scalars.

4  References

Basic Linear Algebra Subprograms Technical (BLAST) Forum (2001) Basic Linear Algebra Subprograms Technical (BLAST) Forum Standard University of Tennessee, Knoxville, Tennessee http://www.netlib.org/blas/blast-forum/blas-report.pdf

5  Arguments

1:     n IntegerInput
On entry: n, the number of elements in x, y and w.
Constraint: n0.
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 max1,1+n-1×incx.
On entry: the n-element vector x.
If incx>0, xi must be stored in x[i-1×incx], for i=1,2,,n.
If incx<0, xi must be stored in x[n-i×incx], for i=1,2,,n.
Intermediate elements of x are not referenced. If n=0, x is not referenced and may be NULL.
4:     incx IntegerInput
On entry: the increment in the subscripts of x between successive elements of x.
Constraint: incx0.
5:     beta doubleInput
On entry: the scalar β.
6:     y[dim] const doubleInput
Note: the dimension, dim, of the array y must be at least max1,1+n-1×incy.
On entry: the n-element vector y.
If incy>0, yi must be stored in y[i-1×incy], for i=1,2,,n.
If incy<0, yi must be stored in y[n-i×incy], for i=1,2,,n.
Intermediate elements of y are not referenced. If β=0.0 or n=0, y is not referenced and may be NULL.
7:     incy IntegerInput
On entry: the increment in the subscripts of y between successive elements of y.
Constraint: incy0.
8:     w[dim] doubleOutput
Note: the dimension, dim, of the array w must be at least max1,1+n-1×incw.
On exit: the n-element vector w.
If incw>0, wi is in w[i-1×incw], for i=1,2,,n.
If incw<0, wi is in w[n-i×incw], for i=1,2,,n.
Intermediate elements of w are not referenced.
9:     incw IntegerInput
On entry: the increment in the subscripts of w between successive elements of w.
Constraint: incw0.
10:   fail NagError *Input/Output
The NAG error argument (see Section 2.7 in How to Use the NAG Library and its Documentation).

6  Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
See Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.
NE_BAD_PARAM
On entry, argument value had an illegal value.
NE_INT
On entry, incw=value.
Constraint: incw0.
On entry, incx=value.
Constraint: incx0.
On entry, incy=value.
Constraint: incy0.
On entry, n=value.
Constraint: n0.
NE_INTERNAL_ERROR
An unexpected error has been triggered by this function. Please contact NAG.
See Section 2.7.6 in How to Use the NAG Library and its Documentation for further information.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.

7  Accuracy

The BLAS standard requires accurate implementations which avoid unnecessary over/underflow (see Section 2.7 of Basic Linear Algebra Subprograms Technical (BLAST) Forum (2001)).

8  Parallelism and Performance

nag_dwaxpby (f16ehc) is not threaded in any implementation.

9  Further Comments

None.

10  Example

This example computes the result of a scaled vector accumulation for
α=3,   x = -6,4.5,3.7,2.1,-4T , β=-1,   y = -5.1,-5,6.4,-2.4,-3T .  
x and y, and also the sum vector w, are stored in reverse order.

10.1  Program Text

Program Text (f16ehce.c)

10.2  Program Data

Program Data (f16ehce.d)

10.3  Program Results

Program Results (f16ehce.r)


nag_dwaxpby (f16ehc) (PDF version)
f16 Chapter Contents
f16 Chapter Introduction
NAG Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2016