[galib] Quick question on mutation probability

Anthony Liekens a.m.l.liekens at tue.nl
Fri Jun 11 03:31:30 EDT 2004

The probability of mutating a bit string is bitwise, similar to 
mutations in nature. pMut = 0.01 means that each bit will be flipped 
with this probability. There is a strictly positive probability that a 
string is not mutated with pMut=0.01, i.e. (1-pMut)^stringLength. There 
is also a very small probability (pMut^stringLength) that all bits in 
the bitstring are flipped. As a result, it is not true that "at leat" 2 
bits out of 200 will be mutated, but "on average" 2 bits will be 
mutated. Assuming a bitwise mutation probability thus gives a mutation 
rate for bitstrings that is proportional with the bitstrings' length, 
i.e. longer bitstrings will, on average, have more bits flipped with a 
constant mutation rate.


>If pMut = 0.01 and my binary string has a length of 200 bits. That means
>that at least two bits are always mutating on every chromosome?
>There is no chromosome that exhibits no change?
>Isn't that bad?
>If I am correct, the pMut should be proportional to the string size.

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