F16ELF (BLAS_DSUM) (PDF version)
F16 Chapter Contents
F16 Chapter Introduction
NAG Library Manual

NAG Library Routine Document

F16ELF (BLAS_DSUM)

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

+ Contents

    1  Purpose
    7  Accuracy

1  Purpose

F16ELF (BLAS_DSUM) sums the elements of a real vector.

2  Specification

FUNCTION F16ELF ( N, X, INCX)
REAL (KIND=nag_wp) F16ELF
INTEGER  N, INCX
REAL (KIND=nag_wp)  X(1+(N-1)*ABS(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  Parameters

1:     N – INTEGERInput
On entry: n, the number of elements in x.
2:     X(1+N-1×INCX) – REAL (KIND=nag_wp) arrayInput
On entry: the vector x. Element xi is stored in Xi-1×INCX+1, for i=1,2,,n.
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  Further Comments

None.

9  Example

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

9.1  Program Text

Program Text (f16elfe.f90)

9.2  Program Data

Program Data (f16elfe.d)

9.3  Program Results

Program Results (f16elfe.r)


F16ELF (BLAS_DSUM) (PDF version)
F16 Chapter Contents
F16 Chapter Introduction
NAG Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2012