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Chapter Contents
Chapter Introduction
NAG Toolbox

# NAG Toolbox: nag_blast_isum (f16dl)

## Purpose

nag_blast_isum (f16dl) sums the elements of an integer vector.

## Syntax

[result] = f16dl(n, x, incx)
[result] = nag_blast_isum(n, x, incx)

## Description

nag_blast_isum (f16dl) returns the sum
 $x1 + x2 + ⋯ + xn$
of the elements of an $n$-element integer vector $x$, via the function name.
If ${\mathbf{n}}\le 0$ on entry, nag_blast_isum (f16dl) immediately returns the value $0$.

## 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

## Parameters

### Compulsory Input Parameters

1:     $\mathrm{n}$int64int32nag_int scalar
$n$, the number of elements in $x$.
2:     $\mathrm{x}\left(1+\left({\mathbf{n}}-1\right)×\left|{\mathbf{incx}}\right|\right)$int64int32nag_int array
The $n$-element vector $x$.
If ${\mathbf{incx}}>0$, ${x}_{\mathit{i}}$ must be stored in ${\mathbf{x}}\left(\left(\mathit{i}-1\right)×\left|{\mathbf{incx}}\right|+1\right)$, for $\mathit{i}=1,2,\dots ,{\mathbf{n}}$.
If ${\mathbf{incx}}<0$, ${x}_{\mathit{i}}$ must be stored in ${\mathbf{x}}\left(\left({\mathbf{n}}-\mathit{i}\right)×\left|{\mathbf{incx}}\right|+1\right)$, for $\mathit{i}=1,2,\dots ,{\mathbf{n}}$.
Intermediate elements of x are not referenced. If ${\mathbf{n}}=0$, x is not referenced.
3:     $\mathrm{incx}$int64int32nag_int scalar
The increment in the subscripts of x between successive elements of $x$.
Constraint: ${\mathbf{incx}}\ne 0$.

None.

### Output Parameters

1:     $\mathrm{result}$int64int32nag_int scalar
The result of the function.

## Error Indicators and Warnings

If ${\mathbf{incx}}=0$, an error message is printed and program execution is terminated.

## 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)).

None.

## Example

This example computes the sum of the elements of
 $x = 1,10,11,-2,9T .$
```

fprintf('f16dl example results\n\n');

% sum vector of integers x
n    = int64(5);
x    = [int64(1)  10  11  -2    9];
incx = int64(1);

xsum = f16dl(n, x, incx);

fprintf('sum(');
fprintf('%4d',x);
fprintf(') = %5d\n',xsum);

```
```f16dl example results

sum(   1  10  11  -2   9) =    29
```