Yes, thank you!
On Sun, Nov 10, 2013 at 2:39 PM, Matthias Felleisen <matth...@ccs.neu.edu>wrote: > > I think this is the program you want: > > #lang racket > > (module+ test > (require rackunit)) > > ;; [List-of Real] -> [List-of Real] > > (module+ test > (check-equal? (roulette-wheel-ratio '(1 2 3)) '(1/6 2/6 3/6))) > > (define (roulette-wheel-ratio generation-fitness) > (define total-population-fitness (foldl + 0 generation-fitness)) > (map (lambda (fitness) (/ fitness total-population-fitness)) > generation-fitness)) > > > > > On Nov 10, 2013, at 2:28 PM, Rian Shams wrote: > > > Hello All, > > > > As part of the design for a simple genetic algorithm I have this > function: > > > > (define (roulette-wheel-ratio generation-fitness ) > > (cond [(empty? generation-fitness) empty] > > [else (cons (/ (first generation-fitness) > > (total-population-fitness > generation-fitness)) > > (roulette-wheel-ratio (rest generation-fitness)))])) > > > > where generation-fitness is a list of values that correspond to the > fitness of each individual in a population. For example, in a generation > with population size 12, generation fitness may look like: > > > > '(7.8807275269175125 > > 6.78896220864992 > > 6.52572681075793 > > 3.208263473483078 > > 9.970710802683316 > > 10.400703374724888 > > 7.434703353949041 > > 6.009574612909729 > > 2.9503066173989634 > > 6.07124467626777 > > 2.1893449585751754 > > 1.0741024515301607) > > > > Here is how I have defined the auxiliary function, > total-population-fitness: > > > > (define (total-population-fitness generation-fitness) > > (foldl + 0 generation-fitness)) > > > > I was wondering how can I modify the above function, > roulette-wheel-ratio so that when it evaluates the helper function, > total-population-fitness it only does so for the initial list of > generation-fitness. Otherwise the total population fitness decreases for > each recursive call which is what I don't want, it should remain constant > throughout the entire function call. > > > > Basically, is it possible to modify this function so that the auxiliary > function call (total-population-fitness generation-fitness) remains > unaffected by the natural recursion imposed by roulette-wheel-ratio? > > > > Any help would be appreciated as I am still learning the Racket basics. > > > > Kind Regards, > > -- > > Rian Shams > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > >
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