roulette:

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   Roulette is the traditional selection function with the probability of
   surviving equal to the fittness of i / sum of the fittness of all 
   individuals.

   Since version 7.
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   Form:
   [newPop] = roulette(oldPop,options)
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   Inputs
   ------  
   oldPop              the current population
   options             options [gen]

   -------
   Outputs
   -------
   newPop              the new population selected from the oldPop

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