How to write noonlinear equality constraints in ga?

Hello,

I am trying to write a "ga" code in matlab. The code without constraint does work correctly. I need to define a constraint as follow:

function [c,ceq] = mycon(~)
global MDLAC
ceq = [];
c = [(MDLAC - 1);
   ((-1)*MDLAC)];
end

which "MDLAC", defines as:

MDLAC = ((abs(delta_f'*round_f))^2)/((delta_f'*delta_f)*(round_f'*round_f));

"delta_f" is a vector consists of numbers, and "round_f" consists of numbers and variables.

Now my problem is that I cannot use both parts of "C" in constraint function. In other words if in constraint function I define "C" as follow:

c = MDLAC - 1;

or

c =(-1)*MDLAC);

the code runs perfectly, but when I use it as I mentioned earlier in this note (as a combination of two terms) the code gives me an error as follow:

Unable to perform assignment because the left and right sides have a different
number of elements.

Error in augLagFun>augLagScalarFun (line 155)
[cin(:),ceq(:)] = feval(nonlcon,points,conFcnArg{:});

Error in augLagFun (line 24)
    lagrangeFval = augLagScalarFun(points,objfun,nonlcon,augLagStruct, ...

Error in createAnonymousFcn>@(x)fcn(x,FcnArgs{:}) (line 11)
fcn_handle = @(x) fcn(x,FcnArgs{:});

Error in makeState (line 47)
            firstMemberScore =
            FitnessFcn(state.Population(initScoreProvided+1,:));

Error in gacon (line 39)
state = makeState(GenomeLength,SubFitness,Iterate,subtype,options);

Error in ga (line 405)
                [x,fval,exitFlag,output,population,scores] =
                gacon(FitnessFcn,nvars, ...

Error in complete_code_3D_2 (line 318)
[x, fval,exitflag,output,population] =
ga(@obj_func_3D,3,[],[],[],[],lb,ub,@mycon,options)

Caused by:
    Failure in initial user-supplied fitness function evaluation. GA cannot
    continue.
    

I will appreciate it so much if you could help me through this. Thank you.