NAG Library Function Document

nag_iamax_val (f16dqc)

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: $n \geq 0$ .
2: x[ $\dim$ ] – const IntegerInput: Note: the dimension, dim, of the array x must be at least $\max (1, 1 + (n - 1) \times |incx|)$ .
On entry: the vector $x$ . Element $x_{i}$ is stored in $x [(i - 1) \times |incx|]$ , for $i = 1, 2, \dots, n$ .
3: incx – IntegerInput: On entry: the increment in the subscripts of x between successive elements of $x$ .
Constraint: $incx \neq 0$ .
4: k – Integer *Output: On exit: $k$ , the index, from the set $\{0, |incx|, \dots, (n - 1) \times |incx|\}$ , of the largest component of $x$ with respect to absolute value. If $n = 0$ on input then k is returned as $-1$ .
5: i – Integer *Output: On exit: $i$ , the largest component of $x$ with respect to absolute value. If $n = 0$ on input then i is returned as $0$ .
6: fail – NagError *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: $incx \neq 0$ .
On entry, $n = ⟨value⟩$ .
Constraint: $n \geq 0$ .

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

Not applicable.

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, 9)}^{T} .

NAG Library Function Documentnag_iamax_val (f16dqc)

+− Contents

1 Purpose

2 Specification

3 Description

4 References