NAG Library Routine Document

F16DRF

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 Parameters

1: $N$ – INTEGERInput: On entry: $n$ , the number of elements in $x$ .
2: $X (1 + (N - 1) \times |INCX|)$ – INTEGER arrayInput: On entry: the $n$ -element vector $x$ .
If $INCX > 0$ , $x_{i}$ must be stored in $X ((i - 1) \times |INCX| + 1)$ , for $i = 1, 2, \dots, N$ .

If $INCX < 0$ , $x_{i}$ must be stored in $X ((N - i) \times |INCX| + 1)$ , for $i = 1, 2, \dots, N$ .

Intermediate elements of X are not referenced. If $N = 0$ , X is not referenced.
3: $INCX$ – INTEGERInput: On entry: the increment in the subscripts of X between successive elements of $x$ .

Constraint: $INCX \neq 0$ .
4: $K$ – INTEGEROutput: On exit: $k$ , the index, from the set $\{1, 1 + |INCX|, \dots, 1 + (N - 1) \times |INCX|\}$ , of the smallest component of $x$ with respect to absolute value. If $N \leq 0$ on input then K is returned as $0$ .
5: $I$ – INTEGEROutput: On exit: $i$ , the smallest component of $x$ with respect to absolute value. If $N \leq 0$ on input then I is returned as $0$ .

6 Error Indicators and Warnings

INCX = 0

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

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 smallest component with respect to absolute value and index of that component for the vector

x = {(1, 10, 11, - 2, 9)}^{T} .

NAG Library Routine DocumentF16DRF

▸▿ Contents

1 Purpose

2 Specification

3 Description

4 References