NAG Library Routine Document

f16elf (blas_dsum) (dsum)

1
Purpose

f16elf (blas_dsum) 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 <nagmk26.h>
double  f16elf_ (const Integer *n, const double x[], const Integer *incx)
The routine may be called by its BLAST name blas_dsum.

3
Description

f16elf (blas_dsum) 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 (blas_dsum) 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:     n – IntegerInput
On entry: n, the number of elements in x.
2:     x1+n-1×incx – Real (Kind=nag_wp) arrayInput
On entry: the n-element vector x.
If incx>0, xi must be stored in xi-1×incx+1, for i=1,2,,n.
If incx<0, xi must be stored in xn-i×incx+1, for i=1,2,,n.
Intermediate elements of x are not referenced. If n=0, x is not referenced.
3:     incx – IntegerInput
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 (blas_dsum) is not threaded in any implementation.

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 (f16elfe.f90)

10.2
Program Data

Program Data (f16elfe.d)

10.3
Program Results

Program Results (f16elfe.r)