Genetic algorithm say 'average change in the fitness value less than options.Fu​nctionTole​rance.'

I am studying 'Genetic algorithm'. I made 'y2' for optimizing with this function ' y = 100 * (a^2 - b) ^2 + (1 - a)^2 '.

Those are same things. like between y = a + 3 and y = 2 + 3. and i want to get a = 2. I thought this way 'sum((y-y2).^2)'.

But it doesn't work well saying ''average change in the fitness value less than options.FunctionTolerance.' The results are not good. I think the iteration is not enough to optimize . and it ends.

How could I solve this problem....

Thank you so much..

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 y2 = 100 * (1.5083^2 - 2.2781) ^2 + (1 - 1.5083)^2;

 rng default % For reproducibility
 FitnessFunction = @(a,b) simple_fitness(y2);
 numberOfVariables = 2;
 lb = [-3 -3];
 ub = [3 3];
 [x,fval] = ga(FitnessFunction,numberOfVariables,[],[],[],[],lb,ub)

 function of = simple_fitness(y2)
 a=1;
 b=1;
 y = 100 * (a^2 - b) ^2 + (1 - a)^2;
 of = sum((y-y2).^2);
 end

Answer 1

[Matt J]

   function of = simple_fitness(y2)

      a=y2(1);
      b=y2(2);

      of = 100 * (a^2 - b) ^2 + (1 - a)^2; 

     end