Simulated Annealing for string matching with Python

Question

I have a problem of implementing a string matching algorithm with SA. After all the iterations are done, I am not getting even closer to the string I want. I tried to decrease the temperature change but nothing has changed.

For me, I think that the problem is because p is not decreasing steadily. The reason I think is that de is changing "randomly". Am I right? If so, how to fix it?

The goal is that the score should reach 0 at the end. The score sums up all the distances between the random letters and the actual ones. change_cur_solution changes only one random letter each time.

def eval_current_sol(target,cur_sol): 
  dist = 0
  for i in range(len(target)): 
    c = cur_sol[i] 
    t = target[i] 
    dist += abs(ord(c) - ord(t)) 
  return dist 


t = 10000
# loop until match the target
it = 0
while True: 
    if t == 0:
       break
    print('Current best score ', bestScore, 'Solution', "".join(bestSol)) 
     
    if bestScore == 0: 
      break
     
    newSol = list(bestSol) 

    change_cur_solution(newSol)
    score = eval_current_sol(newSol,targetSol) 
    de =  score - bestScore

    if de < 0:                  ## score < bestScore i.e. (score of new solution < score of previous solution) ===> #better
        bestSol = newSol 
        bestScore = score
    else:
        r = random.random()
        try:
            p = math.exp(-(de / t))
        except:
            p = 0
        print("p is %f de is %d t is %d" %(p, de,t))
        if p > r:
            bestSol = newSol
            bestScore = score
    it += 1
    t -= 0.5
    
print('Found after, ',it, 'Iterations' ) 

Here is a sample of the code running when t is about 700

Here is another sample run at the end:

Note: a similar code was done with hill climbing and worked fine.

Answer 1

t -= 0.5

Is a linear cooling. This is generally not the best. (?) Have you tried geometric?

t = t * 0.95

Of course, 0.95 is a guess, and you want to explore difference start/stop temp combinations, and cooling factor.