Error & returning a set of values

I have the `test` function shown below written in `matlab`, and underneath the `test` function you can find other functions that the `test` function uses.

Here, I have two points:

*1- When I run the program, I get the following error. Why is that? How can I solve it?*

    ??? Input argument "y" is undefined.

    Error in ==> relative_complement at 2
    rl = setdiff(x,y);

    Error in ==> test at 44
    rl = relative_complement(support, C.(sprintf('Ck')));

*2- As an output, I want the values of `C.(sprintf('Ck'))` to be produced as a set of values rather than only one value. In other words, for each iteration to update the value of `Ck` and get the result as a set. How can I do that?*

*test*

    function test    
    F = [5 3 3 4 ; 5 3 2 4; 6 5 3 6; 6 4 3 3; 8 4 3 6; 7 5 4 3; 87 5 4 3];
    support = [1 3 4 4; 5 4 4 6; 6 5 43 3; 7 4 3 4];
    C = struct;
    n=10;
    for i=1:n
    C.(sprintf('C%d',i)) = [];
    end
    C.(sprintf('Ck')) = [];
    k=0;
    while k<n
    rl = relative_complement(support, C.(sprintf('Ck')));
    pixels = belongs_to(F, rl);
    d = equalize_dimension(F, pixels);
    e = pixel_minimize_distance(d.x, d.y);
    C.(sprintf('Ck')) = e;
    C.(sprintf('Cnew')) = C.(sprintf('Ck'));
    d1 = equalize_dimension(F, C.(sprintf('Cnew')));
    d2 = equalize_dimension(F, C.(sprintf('C%d',k+1)));
    distance_new = distance_between_sets(d1.x, d1.y);
    distance_k_plus_one = distance_between_sets(d2.x, d2.y);
    if isempty(C.(sprintf('C%d',k+1))) | distance_new < distance_k_plus_one
        C.(sprintf('C%d',k+1)) = C.(sprintf('Cnew'));
        C.(sprintf('Ck')) =  C.(sprintf('C%d',k+1));
    end   
    end
     C.(sprintf('Ck'))
    end

*relative_complement*

    function rl = relative_complement(obj,x,y)
        rl = setdiff(x,y);
        end

belongs_to**

    function p = belongs_to(x,y)
    member = ismember(x,y);
    p = x(member==1);
    end

equalize_dimension**

        function n = equalize_dimension (x,y)
                [r1 c1] = size(x);
                [r2 c2] = size(y);

                if r1<r2
                e= r2-r1;
                for i=1:e
                x(r1+1,1)=0;
                r1 = r1 + 1;
                end
                [r1 c1] = size(x);
                n.x =x;
                n.y = y;
                end

                if r1>r2
                e = r1-r2;
                for i=1:e
                y(r2+1,1)=0;
                r2 = r2 + 1;
                end
                [r2 c2] = size(y);
                n.x = x;
                n.y = y;
                end

                if c1<c2
                e= c2-c1;
                for i=1:e
                x(1,c1+1)=0;
                c1 = c1 + 1;
                end
                [r1 c1] = size(x);
                n.x = x;
                n.y = y;
                end

                if c1>c2
                e = c1-c2;
                for i=1:e
                y(1,c2+1)=0;
                c2 = c2 + 1;
                end
                [r2 c2] = size(y);
                n.x = x;
                n.y = y;
                end

                if r1==r2 && c1==c2
                n.x =  x;
                n.y = y;
                end
    end

*pixel_minimize_distance*

    function m = pixel_minimize_distance(x,y)
    maximum = (sum(sum(pdist2(x,y))));
    [r c] = size(y);
    initialValue = y(1,1);
    for i=1:r
        for j=1:c
            o = y(i,j);
            y(i,j) = 0;
            sum2 = (sum(sum(pdist2(x,y))));

            if sum2 >= maximum
                if o ~= 0
                    maximum = sum2;
                    m = o;
                end
            maximum = maximum;
            m = initialValue;
            end
            y(i,j)=o;
        end
        end
    end

distance_between_sets**

    function m = distance_between_sets(x,y)
    [r c] = size(x);
    for i=1:r
         for j=1:c
         summation = (sum(sum(pdist2(x,y))));
         end
    end
         m=summation;
    end

Thanks.