ga optimization changing answer

Hi everyone

I have a question about GA optimization answer.

I want to optimize this function with 5 variable, as below:

Q=ga(@(b) -(-1e-6*((b(1))^2)+5.69e2*(b(1))+...
    -1e-6*((b(2))^2)+8e2*(b(2))+...
    -1e-6*((b(3))^2)+4e2*(b(3))+...
    -1e-6*((b(4))^2)+4e2*(b(4))+...
    -1e-6*((b(5))^2)+5e2*(b(5))),5)

at first i run the code and the answer was what you can see below:

Optimization terminated: maximum number of generations exceeded.

Q =

   1.0e+03 *

    1.6325    2.2597    1.5050    1.4811    1.4940

i run the code for second time and the answer changed to:

Optimization terminated: maximum number of generations exceeded.

Q =

   1.0e+03 *

    1.8045    2.3893    1.4345    1.5154    1.5075

and for the third time the answer was:

Optimization terminated: maximum number of generations exceeded.

Q =

   1.0e+03 *

    1.8864    2.3098    1.4213    1.5103    1.2786    

as you can see, the answer for each run was changed. why is this happening? I know that ga uses several iterations to obtain the answer, but I thought that the final answer is unique and fixed. am I doing something wrong? could you please explain this result for me?

Answer 1

[Chunru]

GA need random initialization of population and it also involves random processing in generating children. Therefore, the results of different run may be different. To make the result reproducible, you need to reset the random generator before each run. For example:

rng default
Q=ga(@(b) -(-1e-6*((b(1))^2)+5.69e2*(b(1))+...
    -1e-6*((b(2))^2)+8e2*(b(2))+...
    -1e-6*((b(3))^2)+4e2*(b(3))+...
    -1e-6*((b(4))^2)+4e2*(b(4))+...
    -1e-6*((b(5))^2)+5e2*(b(5))),5)

Optimization terminated: maximum number of generations exceeded.

Q = 1×5

1.0e+03 * 1.8729 2.0826 1.6439 1.5220 1.7711

rng default
Q=ga(@(b) -(-1e-6*((b(1))^2)+5.69e2*(b(1))+...
    -1e-6*((b(2))^2)+8e2*(b(2))+...
    -1e-6*((b(3))^2)+4e2*(b(3))+...
    -1e-6*((b(4))^2)+4e2*(b(4))+...
    -1e-6*((b(5))^2)+5e2*(b(5))),5)

Optimization terminated: maximum number of generations exceeded.

Q = 1×5

1.0e+03 * 1.8729 2.0826 1.6439 1.5220 1.7711

[shirin mhd]

Thank you very much.