Why is my maxperf.m code not operating correctly

p = [2, 5];
q = [1, 0, 1, 2, 2];
% Call the maxperf function
maxperf(p, q);

dp = 2

extremal_points =

  0×1 empty double column vector


max_J =

  0×1 empty double column vector


index =

  0×1 empty double column vector


maximizing_x =

  0×1 empty double column vector

Maximizing value of x:
Maximal value of J(x):

function maxperf(p, q)
    % Compute the numerator polynomial of the derivative of J(x)
    dp = polyder(p)
    dJ_num = conv(dp, p) - conv(p, dp);

    % Find the critical points where dJ(x)/dx = 0
    extremal_points = roots(dJ_num)

    % Evaluate J(x) at each extremal point
    J_values = polyval(p, extremal_points).^2 ./ polyval(q, extremal_points);

    % Find the maximizing value of J(x) and the corresponding x
    [max_J, index] = max(J_values)
    maximizing_x = extremal_points(index)

    % Display the results
    disp("Maximizing value of x:");
    disp(maximizing_x);
    disp("Maximal value of J(x):");
    disp(max_J);   
end

[lateef]

the error i get when i run the code is in line i am following the instructions of the pdf i attatched

[Image Analyst]

Is this a duplicate of your other post?

https://www.mathworks.com/matlabcentral/answers/1999088-please-review-matlab-code-and-tell-me-why-i-receive-errors#answer_1276743

Answer 1

[Steven Lord]

Move the lines where you define p and q and call maxperf out of the maxperf function. With those lines present, MATLAB will do one of two things.

Case 1:

If you call maxperf with two inputs it will run with those two inputs until it gets to the last line of the function. It will then call maxperf with the p and q vectors you defined inside maxperf as inputs.

It will run with those two inputs until it gets to the last line of the function. It will then call maxperf with the p and q vectors you defined inside maxperf as inputs.

It will run with those two inputs until it gets to the last line of the function. It will then call maxperf with the p and q vectors you defined inside maxperf as inputs.

It will run with those two inputs until it gets to the last line of the function. It will then call maxperf with the p and q vectors you defined inside maxperf as inputs. ...

Hopefully you see the pattern, that this will never stop (except MATLAB will detect the infinite recursion and stop itself with an error before it potentially crashes.)

Case 2:

If you call maxperf with no input argument, MATLAB will not "automatically detect" that you've defined variables p and q inside your function and use those as the inputs. It will instead error indicating you haven't provided enough input arguments to maxperf.

With those lines removed, you're in case 3:

If you call maxperf with two inputs it will run with those two inputs until it gets to the last line of the function. Then it will stop executing.

You probably also want to modify maxperf to return some of the variables you compute inside it, so you can use them in whatever code called maxperf.

[lateef]

are you reffering to the last line of the code ?

[Torsten]

@lateef

I did it for you (see above).