NAG FL Interface
f16elf (dsum)

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1 Purpose

f16elf sums the elements of a real vector.

2 Specification

Fortran Interface
Function f16elf ( n, x, incx)
Real (Kind=nag_wp) :: f16elf
Integer, Intent (In) :: n, incx
Real (Kind=nag_wp), Intent (In) :: x(1+(n-1)*ABS(incx))
C Header Interface
#include <nag.h>
double  f16elf_ (const Integer *n, const double x[], const Integer *incx)
The routine may be called by the names f16elf, nagf_blast_dsum or its BLAST name blas_dsum.

3 Description

f16elf returns the sum
x1 + x2 + + xn  
of the elements of an n-element real vector x, via the function name.
If n0 on entry, f16elf 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

5 Arguments

1: n Integer Input
On entry: n, the number of elements in x.
2: x(1+(n-1)×|incx|) Real (Kind=nag_wp) array Input
On entry: the n-element vector x.
If incx>0, xi must be stored in x((i-1)×incx+1), for i=1,2,,n.
If incx<0, xi must be stored in x((n-i)×|incx|+1), for i=1,2,,n.
Intermediate elements of x are not referenced. If n=0, x is not referenced.
3: incx Integer Input
On entry: the increment in the subscripts of x between successive elements of x.
Constraint: incx0.

6 Error Indicators and Warnings

If incx=0, an error message is printed and program execution is terminated.

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

f16elf is not threaded in any implementation.

9 Further Comments


10 Example

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

10.1 Program Text

Program Text (f16elfe.f90)

10.2 Program Data

Program Data (f16elfe.d)

10.3 Program Results

Program Results (f16elfe.r)