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NAG Toolbox

NAG Toolbox: nag_blast_damin_val (f16jr)

 Contents

    1  Purpose
    2  Syntax
    7  Accuracy
    9  Example

Purpose

nag_blast_damin_val (f16jr) computes, with respect to absolute value, the smallest component of a real vector, along with the index of that component.

Syntax

[k, r] = f16jr(n, x, incx)
[k, r] = nag_blast_damin_val(n, x, incx)

Description

nag_blast_damin_val (f16jr) computes, with respect to absolute value, the smallest component, r, of an n-element real vector x, and determines the smallest index, k, such that
r=xk=minjxj.  

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

Parameters

Compulsory Input Parameters

1:     n int64int32nag_int scalar
n, the number of elements in x.
2:     x1+n-1×incx – double array
The vector x. Element xi is stored in xi-1×incx+1, for i=1,2,,n.
3:     incx int64int32nag_int scalar
The increment in the subscripts of x between successive elements of x.
Constraint: incx0.

Optional Input Parameters

None.

Output Parameters

1:     k int64int32nag_int scalar
k, the index, from the set 1,2,,n , of the smallest component of x with respect to absolute value. If n0 on input then k is returned as 0.
2:     r – double scalar
r, the smallest component of x with respect to absolute value. If n0 on input then r is returned as 0.0.

Error Indicators and Warnings

If 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 smallest component with respect to absolute value and index of that component for the vector
x= 1,10,11,-2,9T .  
function f16jr_example


fprintf('f16jr example results\n\n');

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

[xloc, xmin] = f16jr(n, x, incx);

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


f16jr example results

minabs(  1.0 10.0 11.0 -2.0  9.0) = |x(   1)| =   1.0

PDF version (NAG web site, 64-bit version, 64-bit version)
Chapter Contents
Chapter Introduction
NAG Toolbox

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