NAG Library Routine Document

1Purpose

f16dlf sums the elements of an integer vector.

2Specification

Fortran Interface
 Function f16dlf ( n, x, incx)
 Integer :: f16dlf Integer, Intent (In) :: n, x(1+(n-1)*ABS(incx)), incx
#include nagmk26.h
 Integer f16dlf_ (const Integer *n, const Integer x[], const Integer *incx)

3Description

f16dlf 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, f16dlf immediately returns the value $0$.

4References

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

5Arguments

1:     $\mathbf{n}$ – IntegerInput
On entry: $n$, the number of elements in $x$.
2:     $\mathbf{x}\left(1+\left({\mathbf{n}}-1\right)×\left|{\mathbf{incx}}\right|\right)$ – Integer arrayInput
On entry: the $n$-element vector $x$.
If ${\mathbf{incx}}>0$, ${x}_{\mathit{i}}$ must be stored in ${\mathbf{x}}\left(\left(\mathit{i}-1\right)×{\mathbf{incx}}+1\right)$, 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:     $\mathbf{incx}$ – IntegerInput
On entry: the increment in the subscripts of x between successive elements of $x$.
Constraint: ${\mathbf{incx}}\ne 0$.

6Error Indicators and Warnings

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

7Accuracy

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

8Parallelism and Performance

f16dlf is not threaded in any implementation.

None.

10Example

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

10.1Program Text

Program Text (f16dlfe.f90)

10.2Program Data

Program Data (f16dlfe.d)

10.3Program Results

Program Results (f16dlfe.r)

© The Numerical Algorithms Group Ltd, Oxford, UK. 2017