Task: Evolutionary algorithm






PHP: define('TARGET','METHINKS IT IS LIKE A WEASEL');
define('TBL','ABCDEFGHIJKLMNOPQRSTUVWXYZ ');

define('MUTATE',15);
define('COPIES',30);
define('TARGET_COUNT',strlen(TARGET));
define('TBL_COUNT',strlen(TBL));


function unfitness($a,$b)
{
        $sum=0;
        for($i=0;$i<strlen($a);$i++)
                if($a[$i]!=$b[$i]) $sum++;
        return($sum);
}

function mutate($a)
{
        $tbl=TBL;
        for($i=0;$i<strlen($a);$i++) $out[$i]=mt_rand(0,MUTATE)?$a[$i]:$tbl[mt_rand(0,TBL_COUNT-1)];
        return(implode('',$out));
}


$tbl=TBL;
for($i=0;$i<TARGET_COUNT;$i++) $tspec[$i]=$tbl[mt_rand(0,TBL_COUNT-1)];
$parent[0]=implode('',$tspec);
$best=TARGET_COUNT+1;
$iters=0;
do {
        for($i=1;$i<COPIES;$i++) $parent[$i]=mutate($parent[0]);

        for($best_i=$i=0; $i<COPIES;$i++) {
                $unfit=unfitness(TARGET,$parent[$i]);
                if($unfit < $best || !$i) {
                        $best=$unfit;
                        $best_i=$i;
                }
        }
        if($best_i>0) $parent[0]=$parent[$best_i];
        $iters++;
        print("Generation $iters, score $best: $parent[0]\n");
} while($best);





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