How can I dynamically add optimization variables for me problem in a loop?

Hey :)

I have defined an optimization problem as follows:

prob = optimproblem;

Now I wanna add optimization variables in a loop, such as

for i = 1:10

x = optimvar('Test', 'LowerBound', 0);

end

where within the first iteration, the name of the variable should be x_1, in the second iteration it should be x_2 and so on.

I tried something like this, but it didn`t work:

['x_' int2str(i)] = optimvar(ans, 'LowerBound',0);

My next approach was defining a struct for the variables like the following:

for i = 1:10

ans = mat2str(this_is_a_test(i,:));

ans = regexprep(ans, '\[(.*)\]', '$1');

ans = strrep(ans,' ','');

ans = strcat('Test_', ans);

var = ans;

variables(.var) = optimvar(ans, 'LowerBound',0);

end

After obtaining the struct with my optimization variables, I cannot "transfer" it into prob.Variables

I would be extremely glad if someone could help me with this :)

If you need more information, don't hesitate to ask.

Best regards,

Mike

[Stephen23]

Wouldn't this be much easier if you simply define a vector?. The documentation contains this:

"x = optimvar(name,n) creates an n-by-1 vector of optimization variables."

[Mike]

Hey, thanks for the quick response!

I was thinking of it too, but my problem was, that I couldn't think of a way to create the name vector.

I created a vector (e.g. 3x10 char) and I got this error:

Error using optimvar

Name must be a character vector or a scalar string.

Have you got any idea how to solve this issue?

Thanks in advance! :)

[Stephen23]

"I created a vector (e.g. 3x10 char) "

A 3x10 char is not a vector.

"Have you got any idea how to solve this issue?"

As the error message states, the name must be a character vector or a string scalar.

[Mike]

So there is no solution for the approach with "x = optimvar(name,n)"? Because for my problem it is crucial that I name the variables in a specific way. Like x_1, x_2 and example.

[Mike]

For anyone interested in this topic, I found a solution.

var_names = [];

for i = 1:10

ans = mat2str(this_is_a_test(i,:));

ans = regexprep(ans, '\[(.*)\]', '$1');

ans = strrep(ans,' ','');

ans = strcat('Test_', ans);

var_names = [var_names; ans];

end

var_names = string(var_names);

x = optimvar('x', var_names, 'Type', 'integer');

Thanks a lot!

[Stephen23]

@Mike: what class and content does THIS_IS_A_TEST have?

[Mike]

It's a n*m double. It's content is only consisting of ones and twos.

[Stephen23]

"It's a n*m double. It's content is only consisting of ones and twos."

this_is_a_test = randi(1:2,10,3)

this_is_a_test = 10×3

2 1 1 1 2 2 2 1 1 1 2 1 2 2 2 1 1 1 2 1 2 2 1 1 1 2 1 1 2 2

var_names = [];
for i = 1:10
    ans = mat2str(this_is_a_test(i,:));
    ans = regexprep(ans, '\[(.*)\]', '$1');
    ans = strrep(ans,' ','');
    ans = strcat('Test_', ans);
    var_names = [var_names; ans];
end
V0 = string(var_names)

V0 = 10×1 string array
    "Test_211"
    "Test_122"
    "Test_211"
    "Test_121"
    "Test_222"
    "Test_111"
    "Test_212"
    "Test_211"
    "Test_121"
    "Test_122"

Here is a simpler approach to generate those names:

V1 = "Test_"+join(string(this_is_a_test),"")

V1 = 10×1 string array
    "Test_211"
    "Test_122"
    "Test_211"
    "Test_121"
    "Test_222"
    "Test_111"
    "Test_212"
    "Test_211"
    "Test_121"
    "Test_122"