## How can I store the value at each iteration of a genetic algorithm?

Asked by Sylvain Cornelus

### Sylvain Cornelus (view profile)

on 2 Apr 2019
Latest activity Answered by UNAL

### UNAL (view profile)

on 13 Sep 2019 at 22:27
Accepted Answer by Stephan

### Stephan (view profile)

I have a simple function and two constraints for my genetic algorithm code
ObjFcn = @myFitness;
nvars = 2; %number of variables
LB = [0 0]; %lower bound
UB = [1 13]; %upper bound
ConsFcn = @myConstraints;
[x,fval] = ga(ObjFcn,nvars,[],[],[],[],LB,UB,ConsFcn,opts);
function y = myFitness(x)
y = 100*(x(1)^2-x(2))^2 + (1-x(1))^2;
end
function [c,c_eq] = myConstraints(x)
c = [x(1)*x(2) + x(1) - x(2) + 1.5; 10 - x(1)*x(2)];
c_eq = [];
end
I would like to store the values of x at each function evaluation, as well as keep track of the generation. I've found a similar question here but I don't really understand what the solution meant as it wasn't very clear. I believe I need to tell my fitness function to store values of the GA function so when the GA function reads the fitness function the input parameters at that iteration are saved... but I would like help on how the syntax would work for such a thing. Any help is appreciated!
I've also looked at the GA options and was unable to find help with my specific issue.

### Stephan (view profile)

on 2 Apr 2019

Hi,
you coultd try this way:
[x,fval,vals] = solve_problem
function [x,fval,vals] = solve_problem
ObjFcn = @myFitness;
nvars = 2; %number of variables
LB = [0 0]; %lower bound
UB = [1 13]; %upper bound
ConsFcn = @myConstraints;
iter = 1;
vals = [];
[x,fval] = ga(ObjFcn,nvars,[],[],[],[],LB,UB,ConsFcn);
function y = myFitness(x)
y = 100*(x(1)^2-x(2))^2 + (1-x(1))^2;
vals(iter,1:2) = x;
iter = iter+1;
end
function [c,c_eq] = myConstraints(x)
c = [x(1)*x(2) + x(1) - x(2) + 1.5; 10 - x(1)*x(2)];
c_eq = [];
end
end
After running this you can plot how x(1) and x(2) change over the iterations:
yyaxis left
plot(vals(:,1))
yyaxis right
plot(vals(:,2)) Best regards
Stephan

Sylvain Cornelus

### Sylvain Cornelus (view profile)

on 2 Apr 2019
Thank you Stephan! Exactly what I was looking for. I'll read up on the ga function to figure out how to store the generation.

### UNAL (view profile)

on 13 Sep 2019 at 22:27

You can also extract the data directly from the graph that is obtained by configuring the options:
options = optimoptions('ga','PlotFcn', @gaplotbestf);
After obtaining the graph you can extract ist data:
fig = gcf;
dataObjs = findobj(fig,'-property','YData');
y1 = dataObjs(1).YData;
x1 = dataObjs(1).XData;
figure(7)
plot(x1,y1,'*r')