nag_dsum (f16elc) (PDF version)
f16 Chapter Contents
f16 Chapter Introduction
NAG Library Manual

NAG Library Function Document

nag_dsum (f16elc)

+ Contents

    1  Purpose
    7  Accuracy

1  Purpose

nag_dsum (f16elc) sums the elements of a real vector.

2  Specification

#include <nag.h>
#include <nagf16.h>
double  nag_dsum (Integer n, const double x[], Integer incx, NagError *fail)

3  Description

nag_dsum (f16elc) returns the sum
x1 + x2 + + xn
of the elements of an n-element real vector x.
If n=0 on entry, nag_dsum (f16elc) returns the value 0.

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:     nIntegerInput
On entry: n, the number of elements in x.
Constraint: n0.
2:     x[dim]const doubleInput
Note: the dimension, dim, of the array x must be at least max1,1+n-1×incx.
On entry: the vector x. Element xi is stored in x[i-1×incx], for i=1,2,,n.
3:     incxIntegerInput
On entry: the increment in the subscripts of x between successive elements of x.
Constraint: incx0.
4:     failNagError *Input/Output
The NAG error argument (see Section 3.6 in the Essential Introduction).

6  Error Indicators and Warnings

NE_BAD_PARAM
On entry, argument value had an illegal value.
NE_INT
On entry, incx=value.
Constraint: incx0.
On entry, n=value.
Constraint: n0.

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

Not applicable.

9  Further Comments

None.

10  Example

This example computes the sum of the elements of
x = 1.1,10.2,11.5,-2.7,9.2T .

10.1  Program Text

Program Text (f16elce.c)

10.2  Program Data

Program Data (f16elce.d)

10.3  Program Results

Program Results (f16elce.r)


nag_dsum (f16elc) (PDF version)
f16 Chapter Contents
f16 Chapter Introduction
NAG Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2014