NAG Library Routine Document

F06JLF (IDAMAX)

+− Contents

1 Purpose

9 Example

F06JLF (IDAMAX) computes the index of the absolutely largest component of a real vector.

FUNCTION F06JLF (

INTEGER F06JLF

INTEGER	N, INCX
REAL (KIND=nag_wp)	X(*)

The routine may be called by its BLAS name idamax.

F06JLF (IDAMAX) returns, via the function name, the smallest index

i

such that

|x_{i}| = \max_{j} |x_{j}|

where

x

is an

n

-element real vector scattered with stride INCX.

Lawson C L, Hanson R J, Kincaid D R and Krogh F T (1979) Basic linear algebra supbrograms for Fortran usage ACM Trans. Math. Software 5 308–325

1: N – INTEGERInput: On entry: $n$ , the number of elements in $x$ .
2: X( $*$ ) – REAL (KIND=nag_wp) arrayInput: Note: the dimension of the array X must be at least $\max (1, 1 + (N - 1) \times INCX)$ .
On entry: the $n$ -element vector $x$ . $x_{i}$ must be stored in $X (1 + (i - 1) \times INCX)$ , for $i = 1, 2, \dots, N$ .
Intermediate elements of X are not referenced.
3: INCX – INTEGERInput: On entry: the increment in the subscripts of X between successive elements of $x$ .
Constraint: $INCX > 0$ .