F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

# NAG Library Routine DocumentF06JLF (IDAMAX)

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

## 1  Purpose

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

## 2  Specification

 FUNCTION F06JLF ( N, X, INCX)
 INTEGER F06JLF
 INTEGER N, INCX REAL (KIND=nag_wp) X(*)
The routine may be called by its BLAS name idamax.

## 3  Description

F06JLF (IDAMAX) returns, via the function name, the smallest index $i$ such that
 $xi=maxjxj$
where $x$ is an $n$-element real vector scattered with stride INCX.

## 4  References

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

## 5  Parameters

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 $\mathrm{max}\phantom{\rule{0.125em}{0ex}}\left(1,1+\left({\mathbf{N}}-1\right)×{\mathbf{INCX}}\right)$.
On entry: the $n$-element vector $x$. ${x}_{\mathit{i}}$ must be stored in ${\mathbf{X}}\left(1+\left(\mathit{i}-1\right)×{\mathbf{INCX}}\right)$, for $\mathit{i}=1,2,\dots ,{\mathbf{N}}$.
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: ${\mathbf{INCX}}>0$.

None.

Not applicable.