fmincon, How to fix error "inputs of data type double" ?

Hi,

I am doing a minimization with fmincon

Attached files are my constraint function “con”, objective function “obj”, and solution script “F_main”.

Although my objective function returns a scalar (you can try it), however when trying to solve I’m getting an error:

       ??? Error using ==> fmincon at 234

       FMINCON only accepts inputs of data type double.

       Error in ==> F_main at 14

      [x, fval] = fmincon(F,x0,A,b,Aeq,beq,lb,ub)

The only nonstandard thing that I have is the two equality constraints (two equations instead of one). But even when I used one equation for equality constraint just to check if that what was causing the error, the error still occur.

Please advise what is the source of this error in my script or function, and how can I fix it?

I appreciate considering my humble MATLAB experience.

Yaser

Answer 1

[Walter Roberson]

Aeq cannot be a function. Aeq is for static equality constraints. You need to move those equality constraints over to the second output of a nonlinear constraint function, which you would pass after the options.

However, taking another look at your cons.m those are really static equality constraints that you can write in matrix form. You have

Ceq1 = 176 - 197*x(2) - 186*x(1)
Ceq2 =  906*x(2) - (687*x(1)) +  9.2485e+003
Aeq = @con
beq = [10000, 0];

that should be replaced with

Aeq = [-186, -197;
       -687, 906];
Beq = [10000-176;
       0-9.2485e+003];

Also, note that you used @con but supplied cons.m that has function con inside. However, MATLAB identifies functions by their file name when there is a conflict between the file name and the function name, so if you are going to use cons.m then you need to use @cons rather than @con . With the change I indicate here you should not need the function at all (or of a nonlinear constraint function), but you should take note of this for the future

[Yaser]

Thank you Walter, thank you very much

I fixed it according to your remarks and it works

You made it very clear and easy to follow