NAG Library Routine Document

f16dqf (iamax_val)

1
Purpose

f16dqf computes, with respect to absolute value, the largest component of an integer vector, along with the index of that component.

2
Specification

Fortran Interface
Subroutine f16dqf ( n, x, incx, k, i)
Integer, Intent (In):: n, x(1+(n-1)*ABS(incx)), incx
Integer, Intent (Out):: k, i
C Header Interface
#include <nagmk26.h>
void  f16dqf_ (const Integer *n, const Integer x[], const Integer *incx, Integer *k, Integer *i)

3
Description

f16dqf computes, with respect to absolute value, the largest component, i, of an n-element integer vector x, and determines the smallest index, k, such that
i=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.
2:     x1+n-1×incx – Integer 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.
4:     k – IntegerOutput
On exit: k, the index, from the set 1,2,,n , of the largest component of x with respect to absolute value. If n0 on input then k is returned as 0.
5:     i – IntegerOutput
On exit: i, the largest component of x with respect to absolute value. If n0 on input then i is returned as 0.

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

f16dqf is not threaded in any implementation.

9
Further Comments

None.

10
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 .  

10.1
Program Text

Program Text (f16dqfe.f90)

10.2
Program Data

Program Data (f16dqfe.d)

10.3
Program Results

Program Results (f16dqfe.r)