#### NAME

gatask - solve a task assignment problem via a genetic
algorithm

#### SYNOPSIS

**gatask** **-help**
or
**gatask** **[-specs** *string***]** **[-size** *integer***]** **[-gens** *integer***]**
**[-seed** *integer***]** **[-crate** *double***]** **[-mrate** *double***]**
**[-pbase** *double***]**

#### DESCRIPTION

Use a genetic algorithm to solve a task assignment problem
with user-specified costs. This program illustrates how
GAs can perform combinatorial optimization. Reproduction
of strings entails special crossover and mutation opera-
tions which preserve constraints on the form of feasible
solutions with strings being selected based on fitness.

#### OPTIONS

**-specs** *string*
Problem specification file.
**-size** *integer*
Population size.
**-gens** *integer*
Number of generations.
**-seed** *integer*
Random seed.
**-crate** *double*
Crossover rate.
**-mrate** *double*
Mutation rate.
**-pbase** *double*
Exponentiation base.

#### MISCELLANY

Feasible solutions are represented as an array of LEN
integers which must contain all integers between 0 and LEN
- 1 to denote which person performs which task. As such,
the mutation and crossover operators have to be subtly
redefined so that candidate solutions are still feasible
after they are crossed and mutated.
For mutation, we simply swap two locations in a solution
array.
Crossing two solutions is a little more complicated. Con-
sult the source code to see how it's done in a manner that
preserves the feasibility of the two children while blend-
ing portions of each parent solution.
The fitness function works in three steps. First, the
score of a solution is calculated and denoted the raw fit-
ness. The scaled fitness is then set to pow(PBASE, raw
fitness - worst raw fitness). The normalized fitness is
then set to the scaled fitness divided by the sum of the
scaled fitnesses. Thus the sum of the normalized fit-
nesses must be equal to one while a string with a raw
score of one better than another string is PBASE times as
likely to reproduce, where PBASE is the value supplied
with the -pbase option.

#### BUGS

No sanity checks are performed to make sure that any of
the options make sense.

#### AUTHOR

Copyright (c) 1997, Gary William Flake.
Permission granted for any use according to the standard
GNU ``copyleft'' agreement provided that the author's com-
ments are neither modified nor removed. No warranty is
given or implied.

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