NAG Library Function Document

nag_dmax_val (f16jnc)

 Contents

    1  Purpose
    7  Accuracy

1
Purpose

nag_dmax_val (f16jnc) computes the largest component of a real vector, along with the index of that component.

2
Specification

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

3
Description

nag_dmax_val (f16jnc) computes 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:     n IntegerInput
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 n-element vector x.
If incx>0, xi must be stored in x[i-1×incx], for i=1,2,,n.
If incx<0, xi must be stored in x[n-i×incx], for i=1,2,,n.
Intermediate elements of x are not referenced. If n=0, x is not referenced and may be NULL.
3:     incx IntegerInput
On entry: the increment in the subscripts of x between successive elements of x.
Constraint: incx0.
4:     k Integer *Output
On exit: k, the index, from the set 0,1,,n-1 , of the largest component of x. If n=0 on input then k is returned as -1.
5:     r double *Output
On exit: r, the largest component of x. If n=0 on input then r is returned as 0.0.
6:     fail NagError *Input/Output
The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

6
Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
See Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.
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.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.

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

nag_dmax_val (f16jnc) is not threaded in any implementation.

9
Further Comments

None.

10
Example

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

10.1
Program Text

Program Text (f16jnce.c)

10.2
Program Data

Program Data (f16jnce.d)

10.3
Program Results

Program Results (f16jnce.r)

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