How to display the value of a specific component of the objective function after computation is done?

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William 2023-1-20

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https://ww2.mathworks.cn/matlabcentral/answers/1897950-how-to-display-the-value-of-a-specific-component-of-the-objective-function-after-computation-is-done

评论： William 2023-1-30

采纳的回答： Alan Weiss

在 MATLAB Online 中打开

Good evening,

I was looking through Matlab documentation for genetic algorithm and I found the following example: "Plan Nuclear Fuel Disposal Using Multiobjective Optimization" https://www.mathworks.com/help/gads/multiobjective-nuclear-fuel-disposal.html

After reading through that example, I have a question. Is it possible to display/know the value of a specific component of the objective function for a certain point on the Pareto front after the computation is over?

For instance, if I want to know the value of the objective function "cost" for the first point on the front, the command is:

display(sol(1).cost)

But through this command I get the total cost calculated for the first point.

What if I want to know the value for the third cost component? Is there any way to determine it or not? I tried the following: display(sol(1).cost(3)) but apparently it doesn't work.

Do you have any pointers?

I hope my question is clear. If you need any clarification let me know. I will gladly answer any question and I will be really thankful for any suggestions.

Kind regards,

William

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Walter Roberson 2023-1-22

(I am trying to investigate this, but the script is running very slowly on my machine :( :( :( )

William 2023-1-22

@Walter Roberson unfortunately, I'm aware that that script runs very slowly. In the meantime I tried looking everywhere for similar questions but I couldn't find anything. Please, let me know if you manage to find out something about it. I will greatly appreciate it.

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采纳的回答

Alan Weiss 2023-1-23

在 MATLAB Online 中打开

I'd be very interested to know what you think of the nuclear fuel disposal example.

But to answer your question, let's look at an example that is faster to compute.

x = optimvar("x",1,2,LowerBound=-50,UpperBound=50);

fun(1) = x(1)^4 + x(2)^4 + x(1)*x(2) - x(1)^2*x(2)^2 - 9*x(1)^2;

fun(2) = x(1)^4 + x(2)^4 + x(1)*x(2) - x(1)^2*x(2)^2 + 3*x(2)^3;

prob = optimproblem("Objective",fun);

rng default % For reproducibility

sol = solve(prob)

Solving problem using gamultiobj. Optimization terminated: average change in the spread of Pareto solutions less than options.FunctionTolerance.

sol =

1×18 OptimizationValues vector with properties: Variables properties: x: [2×18 double] Objective properties: Objective: [2×18 double]

Look at the two objective components at the first solution point.

t = sol(1).Objective
Cannot find function "solution.mlx".

Error in ()

Look at just the second objective component at the first solution point.

ob = sol(1).Objective(2)

This is exactly what you tried, and it works fine for me.

Alan Weiss

MATLAB mathematical toolbox documentation

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William 2023-1-30

编辑：William 2023-1-30

@Walter Roberson but how is that possible? I got 11 solutions from solve().

If I use display(sol) I get this:

sol =

1×11 OptimizationValues vector with properties:

Variables properties:

alpha: [5-D double]

beta: [5-D double]

gamma: [5-D double]

s: [5×6×11×11 double]

sigma: [5-D double]

w: [5×9×11×11 double]

Objective properties:

psi_time: [355.2000 386.0000 423.0000 444.3000 482.8000 590.1000 506.6000 … ]

psi_energy: [6.0263e+03 5.8362e+03 5.1067e+03 4.8756e+03 4.7247e+03 … ]

Constraints properties:

cons2: [5-D double]

cons6: [5×6×11×11 double]

cons7: [5×9×11×11 double]

cons8: [6×11×11 double]

cons9: [5×11×11 double]

cons10: [5-D double]

cons11: [5-D double]

cons12: [6×11×11 double]

cons13: [5-D double]

cons1: [1×9×11×11 double]

cons3: [5×1×11×11 double]

So I suppose it managed to find several solutions.

However, if I click on "sol" in the workspace, I first get a 1x11 matrix and in each cell "1x11 OptimizationValues", by clicking on a single cell I then get an empty sol(1,1). But this thing happened with the several examples I ran without changing the code so I thought it was something that happened regularly.

All the other commands work just fine. For instance, if I write display(sol(1).psi_time) I get the correct value for objective psi_time at solution point 1. Same goes if I display the values of the decision variables for a certain solution point.

So I don't really understand where the issue lies.

William 2023-1-30

@Alan Weiss thank you again for your help! I really appreciate it.

William 2023-1-30

@Walter Roberson thank you for your suggestions. They work perfectly as intended.

Have a good day!

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