Question

is it possible to evaluate each individual in the population using the fitness value without finding the probability as the following pseudo code

For all members of population
    sum += fitness ( member)
End for 
Loop until new population is full 
      Do this twice 
            Number = Random between 0 and sum
            Currentfitness = 0.0
            For each member in population
               Currentfitness += fitness (member)
               if Number > Currentfitness then select member
            End for 
      End
Create offspring 
End loop

and what the following part of the code do ?

Do this twice

I really confuse how the Roulette Wheel selects pair of parents. can any help ? thanks in advance

Answer 1

The code is meant to select a random element, but with probabilities according to a certain weight.

Example:

• We want to select from a two-element array with the following weights: { 1, 9 }
• The cumulative weight is { 1, 10 }
• The total weight is 10
• We choose a random number between 1 and 10
• We look into the cumulative weight array and find the first index where our random number is
  greater than the element
• This index is the index of the randomly chosen element

Intuitively, this example makes sense: 9 out of ten times the random number will fall between 1 and 9 causing the first element to be drawn with probability 0.9 (just as the weights specified).