calclulate F-statistic (F-test) on a custom fit

I have been looking around and so far I can´t find a solution to this problem. I have a time-series like data set and wrote some code fit the data to a custom fit:

fo_ = fitoptions('method','NonlinearLeastSquares','Lower',[-Inf               -Inf               -Inf               -Inf               -Inf 11.999000000000001 5.9989999999999997],'Upper',[Inf Inf Inf Inf Inf  12   6]);
    ok_ = isfinite(Mes) & isfinite(P);
    if ~all( ok_ )
        warning( 'GenerateMFile:IgnoringNansAndInfs',...
            'Ignoring NaNs and Infs in data.' );
    end
    st_ = [0.76574705281324407 0.5312095858606708 0.56903281101487801 0.11028936943862044 0.15894025687112179 0.111780179282573 0.037518452744076058 ];
    set(fo_,'Startpoint',st_);
    ft_ = fittype('a0+a1*cos(2*pi*x/c1)+b1*sin(2*pi*x/c1)+a2*cos(2*pi*x/c2)+b2*sin(2*pi*x/c2)',...
        'dependent',{'y'},'independent',{'x'},...
        'coefficients',{'a0', 'a1', 'a2', 'b1', 'b2', 'c1', 'c2'});

Now I need to apply an F-test in order to get a measure of how well the model represents the data ( other estatistic than the ones given by [gof]=...) but I cant find much info on how to do a f-Test on a custom nonlinear model.

Any help or advice will be apreciated