========================================================================
PISA  (www.tik.ee.ethz.ch/pisa/)
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Computer Engineering (TIK)
ETH Zurich	 
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NSGA2 - Nondominated Sorting GA II

Implementation in C for the selector side.

Documentation
  
file: nsga2_documentation.txt
author: Marco Laumanns, laumanns@tik.ee.ethz.ch
last change: $date$
========================================================================



The Optimizer
=============

NSGA2 in an elitist multiobjective evolutionary algorithm and has been
proposed by Prof. Kalyanmoy Deb at the KanGAL. Here, we present a
PISA-implementation of the algorithm based on the description in the
cited paper. 

@InProceedings{DAPM2000,
  author = {K. Deb and Samir Agrawal and Amrit Pratap and T. Meyarivan},
   title = {A Fast Elitist Non-Dominated Sorting Genetic Algorithm for
                  Multi-Objective Optimization: {NSGA-II}}, 
   booktitle = {Parallel Problem Solving from Nature -- {PPSN VI}},
   pages = {849--858},
   year = {2000},
   editor = {Marc Schoenauer and K. Deb and G.
                  Rudolph and Xin Yao and Evelyne Lutton and Juan
                  Julian Merelo and Hans-Paul Schwefel},
   address = {Berlin},
   publisher = {Springer}
}


The Parameters
==============

NSGA2 uses the following values for the common parameters.
These parameters are specified in 'PISA_cfg'.

alpha    (population size)
mu       (number of parent individuals)
lambda   (number of offspring individuals)
dim      (number of objectives)



NSGA2 takes two local parameter which is given in a parameter
file. The name of this parameter file is passed to NSGA2 as command
line argument. (See 'nsga2_param.txt' for an example.)

seed         (seed for the random number generator)
tournament   (tournament size for mating selection)



Source Files
============

The source code for LOTZ is divided into four files:

'nsga2.h' is the header file.

'nsga2.c' contains the main function and implements the control flow.

'nsga2_io.c' implements the file i/o functions.

'nsga2_functions.c' implements all other functions including the
selection.

Additionally a Makefile, a PISA_configuration file with common
parameters and a PISA_parameter file with local parameters are
contained in the tar file.

Depending on whether you compile on Windows or on Unix (any OS having
<unistd.h>) uncomment the according '#define' in the 'spea2.h' file.


Usage
=====

Start NSGA2 with the following arguments:

nsga2 paramfile filenamebase poll

paramfile: specifies the name of the file containing the local
parameters (e.g. nsga2_param.txt)

filenamebase: specifies the name (and optionally the directory) of the
communication files. The filenames of the communication files and the
configuration file are built by appending 'sta', 'var', 'sel','ini',
'arc' and 'cfg' to the filenamebase. This gives the following names for
the 'PISA_' filenamebase:

PISA_cfg - configuration file
PISA_ini - initial population
PISA_sel - individuals selected for variation (PISA_
PISA_var - variated individuals (offspring)
PISA_arc - individuals in the archive


Caution: the filenamebase must be consistent with the name of
the configuration file and the filenamebase specified for the NSGA2
module.

poll: gives the value for the polling time in seconds (e.g. 0.5). This
      polling time must be larger than 0.01 seconds.




Limitations
===========

None limitations are known so far.



Stopping and Resetting
======================

The behaviour in state 5 and 9 is not determined by the interface but
by each variator module specifically. NSGA2 behaves as follows:

state 5 (= variator terminated): set state to 6 (terminate as well).
state 9 (= variator resetted): set state to 10 (reset as well).