NAG Library Routine Document

F16JQF (BLAS_DAMAX_VAL)

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: $X (1 + (N - 1) \times |INCX|)$ – REAL (KIND=nag_wp) arrayInput: On entry: the vector $x$ . Element $x_{i}$ is stored in $X ((i - 1) \times |INCX| + 1)$ , for $i = 1, 2, \dots, n$ .
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 largest component of $x$ with respect to absolute value. If $N \leq 0$ on input then K is returned as $0$ .
5: $R$ – REAL (KIND=nag_wp)Output: On exit: $r$ , the largest component of $x$ with respect to absolute value. If $N \leq 0$ on input then R is returned as $0.0$ .

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

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

NAG Library Routine DocumentF16JQF (BLAS_DAMAX_VAL)

▸▿ Contents

1 Purpose

2 Specification

3 Description

4 References