NAG Library Routine Document

f16dqf (iamax_val)

1

Purpose

2

Specification

3

Description

4

References

5

Arguments

1:     $\mathbf{n}$ – IntegerInput

On entry: $n$, the number of elements in $x$.

2:     $\mathbf{x}\left(1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incx}\right|\right)$ – Integer arrayInput

On entry: the $n$-element vector $x$.

If $\mathbf{incx}>0$, $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left(\left(\mathit{i}-1\right)\times \mathbf{incx}+1\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

If $\mathbf{incx}<0$, $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left(\left(\mathbf{n}-\mathit{i}\right)\times \left|\mathbf{incx}\right|+1\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

Intermediate elements of x are not referenced. If $\mathbf{n}=0$, x is not referenced.

3:     $\mathbf{incx}$ – IntegerInput

On entry: the increment in the subscripts of x between successive elements of $x$.

Constraint: $\mathbf{incx}\ne 0$.

4:     $\mathbf{k}$ – IntegerOutput

On exit: $k$, the index, from the set $\left\{1,2,\dots ,\mathbf{n}\right\}$, of the largest component of $x$ with respect to absolute value. If $\mathbf{n}\le 0$ on input then k is returned as $0$.

5:     $\mathbf{i}$ – IntegerOutput

On exit: $i$, the largest component of $x$ with respect to absolute value. If $\mathbf{n}\le 0$ on input then i is returned as $0$.

6

Error Indicators and Warnings

7

Accuracy

8

Parallelism and Performance

9

Further Comments

10

Example

10.1

Program Text

Program Text (f16dqfe.f90)

10.2

Program Data

Program Data (f16dqfe.d)

10.3

Program Results

Program Results (f16dqfe.r)