Problem in using Genetic algorithm tool - Not enough input arguments

I want to use GA to find the minimum of the function z=x^2+y^2.

I define the function:

function z=my_fun(x,y)

z=x.^2+y^2;

then I call the ga function:

ga(@my_fun,2)

but error occurs.

the error message is:

Error using my_fun (line 2) Not enough input arguments.

Error in validate>@(x)fitness(x,FitnessFcnArgs{:}) (line 136) fitness = @(x) fitness(x,FitnessFcnArgs{:});

Error in fcnvectorizer (line 14) y(i,:) = feval(fun,(pop(i,:)));

Error in makeState (line 47) Score = fcnvectorizer(state.Population(initScoreProvided+1:end,:),FitnessFcn,1,options.SerialUserFcn);

Error in gaunc (line 41) state = makeState(GenomeLength,FitnessFcn,Iterate,output.problemtype,options);

Error in ga (line 351) [x,fval,exitFlag,output,population,scores] = gaunc(FitnessFcn,nvars, ...

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

Could someone help me?