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# Mutation Algorithms for String Manipulation (GA)

• Last Updated : 04 Sep, 2018

Genetic Algorithms(GAs) are adaptive heuristic search algorithms that belong to the larger part of evolutionary algorithms. In each generation chromosomes(our solution candidates) undergo mutation and crossover and then selection to produce a better population whose candidates are nearer to our desired solution. Mutation Operator is a unary operator and it needs only one parent to work on. It does so by selecting a few genes from our selected chromosome and apply the desired algorithm.

In this article, I will be talking five Mutation Algorithms for string manipulation –
1) Bit Flip Mutation
2) Random Resetting Mutation
3) Swap Mutation
4) Scramble Mutation
5) Inversion Mutation

Bit Flip Mutation is mainly used for bit string manipulation while others can be used for any
kind of strings. Here our chromosome will be represented as an array and each index will represent one gene. Strings can be represented as an array of characters which in turn is an array of ASCII or numeric values.

Bit Flip Mutation —

In bit flip mutation, we select one or more genes (array indices) and flip their values i.e. we change 1s to 0s and vice versa. It is better explained using the given diagram.

Random Resetting Mutation —

In random resetting mutation, we select one or more genes (array indices) and replace their values with another random value from their given ranges. Let’s say a[i] (an array index / gene) ranges from [1, 6] then random resetting mutation will select one value from [1, 6] and replace a[i]’s value with it.

Swap Mutation —

In Swap Mutation we select two genes from our chromosome and interchange their values.

Scramble Mutation —

In Scramble Mutation we select a subset of our genes and scramble their value. The selected genes may not be contiguous (see the second diagram).

Inversion Mutation —

In Inversion Mutation we select a subset of our genes and reverse their order. The genes have to be contiguous in this case (see the diagram).

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