nag_damax_val (f16jqc) (PDF version)
f16 Chapter Contents
f16 Chapter Introduction
NAG C Library Manual

NAG Library Function Document

nag_damax_val (f16jqc)

+ Contents

    1  Purpose
    7  Accuracy

1  Purpose

nag_damax_val (f16jqc) computes, with respect to absolute value, the largest component of a real vector, along with the index of that component.

2  Specification

#include <nag.h>
#include <nagf16.h>
void  nag_damax_val (Integer n, const double x[], Integer incx, Integer *k, double *r, NagError *fail)

3  Description

nag_damax_val (f16jqc) computes, with respect to absolute value, the largest component, r, of an n-element real vector x, and determines the smallest index, k, such that
r=xk=maxjxj.

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:     nIntegerInput
On entry: n, the number of elements in x.
Constraint: n0.
2:     x[dim]const doubleInput
Note: the dimension, dim, of the array x must be at least max1,1+n-1×incx.
On entry: the vector x. Element xi is stored in x[i-1×incx], for i=1,2,,n.
3:     incxIntegerInput
On entry: the increment in the subscripts of x between successive elements of x.
Constraint: incx0.
4:     kInteger *Output
On exit: k, the index, from the set 0,incx,,n-1×incx , of the largest component of x with respect to absolute value. If n=0 on input then k is returned as -1.
5:     rdouble *Output
On exit: r, the largest component of x with respect to absolute value. If n=0 on input then r is returned as 0.0.
6:     failNagError *Input/Output
The NAG error argument (see Section 3.6 in the Essential Introduction).

6  Error Indicators and Warnings

NE_BAD_PARAM
On entry, argument value had an illegal value.
NE_INT
On entry, incx=value.
Constraint: incx0.
On entry, n=value.
Constraint: n0.

7  Accuracy

Not applicable.

8  Further Comments

None.

9  Example

This example computes the largest component with respect to absolute value and index of that component for the vector
x= 1,10,11,-2,9T .

9.1  Program Text

Program Text (f16jqce.c)

9.2  Program Data

Program Data (f16jqce.d)

9.3  Program Results

Program Results (f16jqce.r)


nag_damax_val (f16jqc) (PDF version)
f16 Chapter Contents
f16 Chapter Introduction
NAG C Library Manual

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