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

Parameters

Compulsory Input Parameters

1: $n$ – int64int32nag_int scalar: $n$ , the number of elements in $x$ .
2: $x (1 + (n - 1) \times |incx|)$ – double array: The vector $x$ . Element $x_{i}$ is stored in $x ((i - 1) \times |incx| + 1)$ , for $i = 1, 2, \dots, n$ .
3: $incx$ – int64int32nag_int scalar: The increment in the subscripts of x between successive elements of $x$ .

Constraint: $incx \neq 0$ .

Optional Input Parameters

None.

Output Parameters

1: $k$ – int64int32nag_int scalar: $k$ , the index, from the set $\{1, 2, \dots, n\}$ , of the largest component of $x$ with respect to absolute value. If $n \leq 0$ on input then k is returned as $0$ .
2: $r$ – double scalar: $r$ , the largest component of $x$ with respect to absolute value. If $n \leq 0$ on input then r is returned as $0.0$ .

Error Indicators and Warnings

incx = 0

, an error message is printed and program execution is terminated.

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)).

Further Comments

None.

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} .

Open in the MATLAB editor: f16jq_example

function f16jq_example


fprintf('f16jq example results\n\n');

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

[xloc, xmax] = f16jq(n, x, incx);

fprintf('maxabs(');
fprintf('%5.1f',x);
fprintf(') = |x(%4d)| = %5.1f\n', xloc, xmax);

f16jq example results

maxabs(  1.0 10.0 11.0 -2.0  9.0) = |x(   3)| =  11.0

PDF version (NAG web site, 64-bit version, 64-bit version)

Chapter Contents

Chapter Introduction

NAG Toolbox