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Corrected a few bugs after the first "public" presentation

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<title>Genetic Engine</title>
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<body>
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<a href="eoTopDown.html">Top-Down page</a> - <a href="eoBottomUp.html">Bottom-up
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<hr WIDTH="100%">
<center>
<h1>
<b><font color="#CC0000">Evolution Engine</font></b></h1></center>
@ -27,33 +28,156 @@ Replacement</li>
Popular evolution engines</li>
</ul>
<p><br>The term evolution engine denotes the different parts that simulate
the Darwinism in Evolutionary Algorithms.<font color="#33CC00"></font>
<p><br><b><font color="#000099"><font size=+2>Introduction</font></font></b>
<br>The term evolution engine denotes the different parts that simulate
the Darwinism in Evolutionary Algorithms.
<center>
<p><i><font color="#33CC00">The fittest individuals are more likely to
<p><i><font color="#009900">The fittest individuals are more likely to
reproduce and survive.</font></i></center>
<p>Darwinism takes place in two different phases of an EA, though in many
<a href="#popular">popular variants</a>, only one phase is activated.
<a href="#popular">popular
variants</a>, only one phase is activated.
<p><a href="#selection">Selection</a> is the Darwinistic choice of parents
that will be allowed to <font color="#33CC00">reproduce</font><font color="#CC33CC">.</font>
that will be allowed to <b><font color="#009900">reproduce</font></b><font color="#CC33CC">.</font>
<br><a href="#replacement">Replacement</a> takes place after reproduction,
and is the Darwinistic choice of those individuals that will <font color="#33CC00">survive</font>,
and is the Darwinistic choice of those individuals that will <b><font color="#009900">survive</font></b>,
i.e. become the parents of the next generation.
<p><a NAME="selection"></a><b><font color="#000099"><font size=+2>Selection</font></font></b>
<br>&nbsp;
<p><a NAME="replacement"></a><b><font color="#000099"><font size=+2>Replacement</font></font></b>
<br>The replacement phase takes place <font color="#FF6600">after the birth
of all offspring</font> through variation operators. The idea is to close
the generation loop, i.e. to end up with a population of individuals that
will be the initial population of next generation. That population will
be <font color="#FF6600">built upon the old parents and the new-born offspring</font>.
In all algorithms that come up with EO, the <font color="#FF6600">population
size</font> is supposed to be <font color="#FF6600">constant</font> from
one generation to the next one - though nothing stops you from writing
an algorithm with varying population size.
<p><b><font color="#000099">Replacement: </font><font color="#FF0000">The
interface</font></b>
<br>The abstract class for replacement procedures is the functor class
<font color="#009900">eoReplacement</font>,
and the interface for its <tt><font color="#993300">operator()</font></tt>
is
<center>
<p><b><tt><font color="#993300">void operator()(const eoPop&lt;EOT>&amp;
_parents, eoPop&lt;EOT>&amp; _offspring)</font></tt></b></center>
<p>which you could have guessed from the inheritance tree for class <b><font face="Arial,Helvetica"><font size=+1><a href="../../doc/html/class_eoreplacement.html">eoReplacement</a></font></font></b>.,
as you see there that <font color="#009900">eoReplacement</font> derives
from <tt><font color="#993300">class eoBF&lt;const eoPop&lt;EOT>&amp;,
eoPop&lt;EOT>&amp;, void></font></tt>.
<br>This means that it takes <font color="#FF6600">2 populations</font>
(called, for obvious anthropomorphic reasons, _parents and _offspring :-)
and puts the result into population offspring (as _parents is passed as
<b><tt><font color="#993300">const</font></tt></b>ant
population).
<p><b><font color="#FF0000">Note</font></b>: After the replacement step,
all algorithms swap the parents and offspring populations - this is why
the result of the replacement is put into the _offspring population --
the _parents being there untouched until the very last moment.
<p><b><font color="#000099">Replacement: </font><font color="#FF0000">Instances</font></b>
<ul>
<li>
The most straightforward replacement is ... <font color="#FF6600">no replacement</font>,
or, more precisely, <font color="#FF6600">generational replacement</font>:
all offspring replace all parents (used in Holland's and Goldberg's traditional
GAs). In EO, this is implemented in the <b><tt><font color="#009900">eoNoReplacement</font></tt></b>
class, whose <tt><font color="#993300">operator()</font></tt> does ...
<font face="Arial,Helvetica"><font size=+1><a href="../../doc/html/eoreplacement_h-source.html#l00051">exactly
nothing</a></font></font> (remember that _parents and _offspring will be
swapped later on).</li>
<br>&nbsp;
<li>
But the basic type of replacement in EO has two major steps, <font color="#FF6600">merging</font>
both populations of parents and offspring, and <font color="#FF6600">reducing</font>
this big population to the right size. The functor class is called <b><tt><font color="#009900">eoMergeReduce</font></tt></b>.
and it <font face="Arial,Helvetica"><font size=+1><a href="../../doc/html/eoreplacement_h-source.html#l00064">contains
two objects</a></font></font> of respective types <b><font color="#009900">eoMerge</font></b>
and <b><font color="#009900">eoReduce</font></b> and you can probably guess
what each of them actually does :-)</li>
<br>&nbsp;
<p>&nbsp;
<p>Available <font color="#FF6600">instances of eoMerge</font> objects
are <b><tt><font color="#009900">eoPlus</font></tt></b>, that simply adds
the parents to the offspring, or <b><tt><font color="#009900">eoElitism</font></tt></b>,
that adds only some of the (best) parents to the offspring. A special case
of eoElistism is <b><tt><font color="#009900">eoNoElitism</font></tt></b>,
an eoMerge that does nothing.
<br>&nbsp;
<p>Available <font color="#FF6600">instances of eoReduce</font> are <b><tt><font color="#009900">eoTruncate</font></tt></b>,
that deterministically keeps only the required number of individuals, taking
the best ones, and <b><tt><font color="#009900">eoEPReduce</font></tt></b>
that usees the EP stocahstic tournamenent to reduce the population.
<p>Available <font color="#FF6600">instances of eoMergeReduce</font> replacement
procedures are built on the above, and include
<ul>
<li>
<b><tt><font color="#009900">eoCommaReplacement</font></tt></b>, one of
the two standard strategies in <font color="#FF6600">Evolution Strategies</font>,
selects the best offspring. It is an <b><tt><font color="#993300">eoMergeReduce(eoNoElitism,
eoTruncate)</font></tt></b>.</li>
<li>
<b><tt><font color="#009900">eoPlusReplacement</font></tt></b>, the other
standard <font color="#FF6600">Evolution Startegies</font> replacement,
where the best from offspring+parents become the next generation. It is
an <b><tt><font color="#993300">eoMergeReduce(eoPlus, eoTruncate)</font></tt></b>.</li>
<li>
<b><tt><font color="#009900">eoEPReplacement</font></tt></b>, from <font color="#FF6600">Evolutionary
Programming</font> historical algorithm, doing a stochastic tournament
among parents + offspring. It is an <b><tt><font color="#993300">eoMergeReduce(eoPlus,
eoEPReduce)</font></tt></b>.</li>
</ul>
<li>
Another type of eoReplacement is eoKillReplace in which some individuals
of the population are reaplced by some of the offspring.</li>
</ul>
<p><br><b><font color="#000099">Replacement: </font><font color="#FF0000">Adding
(weak) elitism</font></b>
<br>You can add what is called <font color="#FF6600">weak elitism</font>
to any replacement by encapsulating it into an <b><tt><font color="#009900">eoWeakElitismReplacement</font></tt></b>
object. Weak elitism ensures that the overall <font color="#FF6600">best
fitness</font> in the population <font color="#FF6600">will never decrease</font>:
if the best fitness in the new population is less than the best fitness
of the parent population, then the best parent is added back to the new
population, replacing the worse.
<p>Within EO, this is very easy to add:
<p>First, declare your replacement functor (here, generational, but it
can be any replacement object):
<br><b><tt><font color="#009900">eoNoReplacement&lt;Indi> genReplace;</font></tt></b>
<br>Then wrap the weak elitism around it:
<br><b><tt><font color="#009900">eoWeakElitismReplacement&lt;Indi> replace(genReplace);</font></tt></b>
<br>and use now replace as your replacement procedure within your algorithm.
<p><font color="#FF0000">Note</font>: of course, adding weak elitism to
an elitist replacement makes no sense - but will not harm either :-)
<p><a NAME="popular"></a><b><font color="#000099"><font size=+2>Popular
evolution engines</font></font></b>
<br>&nbsp;
<br>&nbsp;
<p>
<br>The most popular evolution engines are listed below, together with
the way to use them in EO. If you don't find your particuler algorithm,
please send it to us, and we might include it here!
<ul>
<li>
Generational Genetic Algorihtm</li>
</ul>
<p><br>
<hr WIDTH="100%"><a href="eoTopDown.html">Top-Down page</a> - <a href="eoBottomUp.html">Bottom-up
page</a> - <a href="eoProgramming.html">Programming hints</a> -<b><font face="Arial,Helvetica"><font size=+1><a href="../../doc/html/index.html">EO
documentation</a></font></font></b>
<br>
<hr>
<address>
<a href="mailto:marc@cmapx.polytechnique.fr">Marc Schoenauer</a></address>
<a href="mailto:Marc.Schoenauer@polytechnique.fr">Marc Schoenauer</a></address>
<br><!-- Created: Mon Oct 30 18:15:16 CET 2000 --><!-- hhmts start -->Last
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