Task: Evolutionary algorithm







Python: from string import letters
from random import choice, random
 
target  = list("METHINKS IT IS LIKE A WEASEL")
charset = letters + ' '
parent  = [choice(charset) for _ in range(len(target))]
minmutaterate  = .09
C = range(100)
 
perfectfitness = float(len(target))
    
def fitness(trial):
    'Sum of matching chars by position'
    return sum(t==h for t,h in zip(trial, target))
 
def mutaterate():
    'Less mutation the closer the fit of the parent'
    return 1-((perfectfitness - fitness(parent)) / perfectfitness * (1 - minmutaterate))
 
def mutate(parent, rate):
    return [(ch if random() <= rate else choice(charset)) for ch in parent]
 
def que():
    '(from the favourite saying of Manuel in Fawlty Towers)'
    print ("
           (iterations, fitness(parent)*100./perfectfitness, ''.join(parent)))

def mate(a, b):
    place = 0
    if choice(xrange(10)) < 7:
        place = choice(xrange(len(target)))
    else:
        return a, b
    
    return a, b, a[:place] + b[place:], b[:place] + a[place:]

iterations = 0
center = len(C)/2
while parent != target:
    rate = mutaterate()
    iterations += 1
    if iterations % 100 == 0: que()
    copies = [ mutate(parent, rate) for _ in C ]  + [parent]
    parent1 = max(copies[:center], key=fitness)
    parent2 = max(copies[center:], key=fitness)
    parent = max(mate(parent1, parent2), key=fitness)
que()




Fortran:  
 	module evolve_routines
 
 	implicit none
 	
 	
 	character(len=*),parameter :: targ = 'METHINKS IT IS LIKE A WEASEL'
 	
 	contains
 
 	
 
 	pure elemental function fitness(member) result(n)
 
 
 
 
 	
 	implicit none
 	integer :: n
 	character(len=*),intent(in) :: member
 	
 	integer :: i
 	
 	n=0
 	do i=1,len(targ)
 		n = n + abs( ichar(targ(i:i)) - ichar(member(i:i))  )
 	end do
 	
 
 	end function fitness
 
 	
 
 	pure elemental subroutine mutate(member,factor)
 
 
 
 	
 	implicit none
 	character(len=*),intent(inout) :: member   
 	real,intent(in) :: factor                  
 	
 	integer,parameter :: n_chars = 27	
 	character(len=n_chars),parameter :: chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ '
 	
 	real    :: rnd_val
 	integer :: i,j,n
 	
 	n = len(member)
 		
 	do i=1,n
 		rnd_val = rand()
 		if (rnd_val<=factor) then   
 			rnd_val = rand()
 			j = int(rnd_val*n_chars)+1   
 			member(i:i) = chars(j:j)
 		end if
 	end do
 	
 
	end subroutine mutate
 

 
 	end module evolve_routines
 
 
 
 	program evolve
 
 
 
 	use evolve_routines
 	
 	implicit none
 	
 	
 	integer,parameter :: seed = 12345             
 	integer,parameter :: max_iter = 10000         
 	integer,parameter :: population_size = 200    
 	real,parameter    :: factor = 0.04            
 	integer,parameter :: iprint = 5               
 	
 	
 	integer :: i,iter
 	integer,dimension(1) :: i_best
 	character(len=len(targ)),dimension(population_size) :: population
 	
 	
 	call srand(seed)
 	
 	
 	
 	population(1) = 'PACQXJB CQPWEYKSVDCIOUPKUOJY'  
 	iter=0
 		
 	write(*,'(A10,A30,A10)') 'iter','best','fitness'
 	write(*,'(I10,A30,I10)') iter,population(1),fitness(population(1))
 		
 	do 
 	
 		iter = iter + 1 
 		
  		
 		if (mod(iter,iprint)==0) write(*,'(I10,A30,I10)') iter,population(1),fitness(population(1))
		
 		
 		if ( iter>max_iter .or. fitness(population(1))==0 ) exit
 	
 		
 		population = population(1)	
 		do i=2,population_size
 			call mutate(population(i),factor)	
 		end do
 	
 		
 		
 		i_best = minloc(fitness(population))
 		population(1) = population(i_best(1))
 		 	
 	end do
 	
 	
 	if (mod(iter,iprint)/=0) write(*,'(I10,A30,I10)') iter,population(1),fitness(population(1))
 	 	
 	if (iter>max_iter) then
 		write(*,*) 'No solution found.'
 	else
 		write(*,*) 'Solution found.'
 	end if
 	
 
 	end program evolve