M01 Chapter Contents
M01 Chapter Introduction
NAG Library Manual

# NAG Library Routine DocumentM01ZBF

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

M01ZBF checks the validity of a permutation.

## 2  Specification

 SUBROUTINE M01ZBF ( IPERM, M1, M2, IFAIL)
 INTEGER IPERM(M2), M1, M2, IFAIL

## 3  Description

M01ZBF can be used to check the validity of user-supplied ranks or indices, without the ranks or indices being corrupted.

None.

## 5  Parameters

1:     IPERM(M2) – INTEGER arrayInput/Output
On entry: elements M1 to M2 of IPERM must be set to values which are supposed to be a permutation of the integers M1 to M2. If they are a valid permutation, the routine exits with ${\mathbf{IFAIL}}={\mathbf{0}}$.
On exit: used as internal workpsace prior to being restored and hence is unchanged.
2:     M1 – INTEGERInput
3:     M2 – INTEGERInput
On entry: the range of elements used in the array IPERM and the range of values in the permutation, as specified under IPERM.
Constraint: $0<{\mathbf{M1}}\le {\mathbf{M2}}$.
4:     IFAIL – INTEGERInput/Output
On entry: IFAIL must be set to $0$, $-1\text{​ or ​}1$. If you are unfamiliar with this parameter you should refer to Section 3.3 in the Essential Introduction for details.
For environments where it might be inappropriate to halt program execution when an error is detected, the value $-1\text{​ or ​}1$ is recommended. If the output of error messages is undesirable, then the value $1$ is recommended. Otherwise, if you are not familiar with this parameter, the recommended value is $0$. When the value $-\mathbf{1}\text{​ or ​}\mathbf{1}$ is used it is essential to test the value of IFAIL on exit.
On exit: ${\mathbf{IFAIL}}={\mathbf{0}}$ unless the routine detects an error or a warning has been flagged (see Section 6).

## 6  Error Indicators and Warnings

If on entry ${\mathbf{IFAIL}}={\mathbf{0}}$ or $-{\mathbf{1}}$, explanatory error messages are output on the current error message unit (as defined by X04AAF).
Errors or warnings detected by the routine:
${\mathbf{IFAIL}}=1$
 On entry, ${\mathbf{M2}}<1$, or ${\mathbf{M1}}<1$, or ${\mathbf{M1}}>{\mathbf{M2}}$.
${\mathbf{IFAIL}}=2$
Elements M1 to M2 of IPERM contain a value outside the range M1 to M2.
${\mathbf{IFAIL}}=3$
Elements M1 to M2 of IPERM contain a repeated value.
If ${\mathbf{IFAIL}}={\mathbf{2}}$ or ${\mathbf{3}}$, elements M1 to M2 of IPERM do not contain a permutation of the integers M1 to M2.

Not applicable.

None.

## 9  Example

This example reads in a vector of real numbers, and a vector of ranks; it calls M01ZBF to check the validity of the ranks before calling M01EAF to rearrange the real numbers into the specified order.

### 9.1  Program Text

Program Text (m01zbfe.f90)

### 9.2  Program Data

Program Data (m01zbfe.d)

### 9.3  Program Results

Program Results (m01zbfe.r)