NAG Toolbox: nag_blast_iamax_val (f16dq)

Purpose

Syntax

Description

References

Parameters

Compulsory Input Parameters

1:     $\mathrm{n}$ – int64int32nag_int scalar

$n$, the number of elements in $x$.

2:     $\mathrm{x}\left(1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incx}\right|\right)$ – int64int32nag_int array

The $n$-element vector $x$.

If $\mathbf{incx}>0$, $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left(\left(\mathit{i}-1\right)\times \left|\mathbf{incx}\right|+1\right)$, 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:     $\mathrm{incx}$ – int64int32nag_int scalar

The increment in the subscripts of x between successive elements of $x$.

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

Optional Input Parameters

None.

Output Parameters

1:     $\mathrm{k}$ – int64int32nag_int scalar

$k$, 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 $0$.

2:     $\mathrm{ii}$ – int64int32nag_int scalar

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

Error Indicators and Warnings

Accuracy

Further Comments

Example

Open in the MATLAB editor: f16dq_example

function f16dq_example


fprintf('f16dq example results\n\n');

% max absolute integer and location
n    = int64(5);
x    = [int64(1)  10   11   -2   9];
incx = int64(1);

[xloc, xmax] = f16dq(n, x, incx);

fprintf('maxabs(');
fprintf('%4d',x);
fprintf(') = |x(%4d)| = %5d\n', xloc, xmax);

f16dq example results

maxabs(   1  10  11  -2   9) = |x(   3)| =    11