Troubleshooting mean square error for loop

This is a homework question that I've been working on for a few days but I'm not getting anywhere with. Basically I'm trying to run a model over a range of values for six different parameters (one at a time for now), find the value of that parameter that yields the minimum mean square error, and reassign the corresponding value in that minimum MSE in the possible range of parameter values (i.e. which value of the parameter yields the min MSE?). What I'm getting is MSE values that go to 10^127 and the minimum MSE is almost 800! When I run this for each parameter and plug in the values, my model performs stunningly awful. I can manually the set the parameters to what I think makes sense and get way better results. But I need to figure out where I'm going wrong. I've added comments below where I'm unsure of what's happening.

        ParThK2Q = [0.0001:0.001:0.1]; %I want to test these parameter values
        nThK2Q = length(ParThK2Q); %use the length to create the loop

        for thK2Q = 1:nThK2Q;  %want to loop over values in ParThK2Q
            %call functions in order
            QQ = function(stuff) %call functions

            Func5(thK2Q) = immse(QQ(thK2Q),Qobs(thK2Q));  %find MSE for each it.
            minF5 = min(Func5(Func5>0));  %find the minimum MSE value
            bestloc5 = find(Func5 == minF5);  %minimum value location
        end

        thK2Q = ParThK2Q(bestloc5); %assign MSE parameter value to variable

Answer 1

[KL]

It's hard to answer without knowing what's happening inside your function but anyway I can give you few tips.

 ParThK2Q = 0.0001:0.001:0.1; %no brackets are needed here
 nThK2Q = length(ParThK2Q); 
 %now initialize other variables
 QQ = zeros(size(ParThK2Q));
 Func5 = zeros(size(ParThK2Q));

and then you probably want to find the minimum MSE outside the loop, so the loop should be

for thK2Q = 1:nThK2Q;  %want to loop over values in ParThK2Q
   %call functions in order
   QQ(1,thK2Q) = function(stuff) %call functions
   Func5(t1,hK2Q) = immse(QQ(1,thK2Q),Qobs(thK2Q));
end

In the above function call, i'm quite unclear what you receive as output in QQ during every iteration. Is it a scalar? a vector? If it's a vector, you might want to use a cell array for QQ.

Then outside the loop maybe,

 {minF5, bestloc5] = min(Func5(Func5>0)); 
 thK2Q = ParThK2Q(bestloc5);