MATLAB R2015a multivariable function optimization

I am trying to minimize an objective function with two variables, using MATLAB R2015a. The objective function is:

      function i3 = fob_2(kp,ti)
      G_P = tf(0.2,[2 4 1]);
      G_TT = tf(0.1,[0.5 1]);
      G_TC = tf(kp*[1 1/ti],[1 0]);
      G_CV = 50;
      G_TA = 0.1;
      G_direct = G_TC * G_CV * G_P;
      G_loop = feedback (G_direct , G_TT);
      G_SYS = G_TA * G_loop;
      SP = 1;
      [DT,time] = step(SP * G_SYS);
      error = SP - DT;
      i3 = trapz(time,error.^2);

I tried a few optimization functions, but none of them seem to work. I always get the error message: "**Not enough input arguments.**" at the fifth line of the function, which is

     G_TC = tf(kp*[1 1/ti],[1 0]);

I tried the following functions, presented by the used syntax (at this point I don't care much about the starting point. I care more about getting an answer and correctly programming the optimization function):

    y=fminimax(fob_2,[1,1])

    y=fminsearch(fob_2,[1,1])

    y=fminunc(fob_2,[1,1])

I am sure that the function is correctly programmed, because when I try to call it with two parameters, something like:

    fob_2(2,5)

MATLAB returns the computed value.

So, the problem is on my end, but I don't see where am I mistaking. Can you help me?

Thank you in advance.

Answer 1

[Walter Roberson]

      fob_2v = @(kt) fob_2(kt(1), kt(2))
      y=fminsearch(fob_2v,[1,1])

[Bogdan]

It worked! Thank you very much!

Can you tell me, please, how did you think this solution? :)

[Walter Roberson]

Lots of experience ;-) This kind of solution gets used a lot.

You should also read http://www.mathworks.com/help/matlab/math/parameterizing-functions.html

[Bogdan]

I understand. Thank you, one more time :)