How can I use structs as x input for Matlabs optimization methods?

My functions look like that:

function area_rectangle = area_rectangle(input_variables)

      if ~isfield(input_variables,'height') || ~isfield(input_variables,'width') 
          area_rectangle = NaN;
      else    
          area_rectangle = input_variables.width * input_variables.height;
      end

Suppose I want to use one of Matlabs optimization methods, e.g. fmincon, and pass a struct as input. How could I do that?

fmincon(@area_rectangle, input_variables, ...)
Error using fmincon (line 224)
FMINCON requires the following inputs to be of data type double: 'X0'.

Thanks in advance! Carolin

Answer 1

[Walter Roberson]

You would not do that. Remember that the optimization routines control the values of x themselves, adjusting its value until the optimum value is found. The optimization routines have no idea how to update a struct.

You would instead use one of the optimization routines that can work on vectors of values, and you would pass the values of the fields as elements of x. For example,

function area = calc_area(x)
  height = x(1,:);
  width = x(2,:);
  area = height .* width;
end

[Carolin Katzschke]

Okay. That was the answer I was looking for. Thank you very much.

Answer 2

[Konstantinos Sofos]

Hi Carolin,

Have you seen Create Problem Structure ?

Regards,

[Carolin Katzschke]

Hi Konstantinos, I had a closer look at the problem structure, but I tried to pass a struct for x/x0. As Walter stated, Matlabs optimization methods only work with double matrices. Thank you for your answer anyway. Regards, Carolin