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parents are different from those expressed in the offspring (compare their
expressions in Figure 10.3).
It is worth emphasizing that this gene-restricted recombination allows a
greater control of the modification mechanism and, consequently, permits a
much finer tuning of all the neural network elements. If we were to use, in
multigenic systems, two-point recombination as it is used in the basic GEA,
that is, disrupting chromosomes anywhere, the fine adjustment of the weights
and thresholds in multigenic systems would be an almost impossible task.
The restriction of two-point recombination to only one gene, however, en-
sures that only this gene is modified and, consequently, that the weights and
thresholds of the remaining genes are kept in place.
Remember, however, that intragenic two-point recombination is not the
only source of recombination in multigenic neural networks: gene recombi-
nation is fully operational in those systems and it can be combined with gene
transposition to propel evolution further through the creation of duplicated
genes. And in unigenic systems, the old one-point and two-point recombina-
tion are also fully operational as no synchronization of weights/thresholds is
necessary.
a.
0123456789012345601234567890123456
TTababaab55239341QDbabbabb40396369-[0]
Qaabbbabb29127879QDbabbaaa36972318-[1]
0123456789012345601234567890123456
aabbbabb291
T
39341QDbabbabb40396369
-[0]
Q
Tababaab552
27879QDbabbaaa36972318-[1]
W
= {-0.78, -0.521, -1.224, 1.891, 0.554, 1.237, -0.444, 0.472, 1.012, 0.679}
0,1
0,2
W
= {-1.553, 1.425, -1.606, -0.487, 1.255, -0.253, -1.91, 1.427, -0.103, -1.625}
W
= {-0.148, 1.83, -0.503, -1.786, 0.313, -0.302, 0.768, -0.947, 1.487, 0.075}
1,1
1,2
W
= {-0.256, -0.026, 1.874, 1.488, -0.8, -0.804, 0.039, -0.957, 0.462, 1.677}
Figure 10.3.
Intragenic two-point recombination in multigenic chromosomes
encoding neural networks.
a)
An event of intragenic two-point recombination
illustrated at the chromosome level. Note that the arrays of weights are not modi-
fied by recombination and that parents and offspring share the same weights.
b)
The sub-NNs codified by the parent chromosomes (facing page).
c)
The sub-NNs
codified by the daughter chromosomes (facing page).
