MSE different in fitnlm vs. manually programmed

Hello,

I was fitting specific model on the specific data with the fitnlm function.

The output structure for this, let's call it mdl, provides except anything else beta and Coefficients.Estimate data.

But when I used I used following my own function to evaluate MSE, which looks as pure as possible:

get_MSE = @(mdlfun, tr_x, tr_y, b) mean((tr_y-mdlfun(b, tr_x)).^2);

... there was little difference between

get_MSE = @(mdlfun, tr_x, tr_y, mdl.Coefficients.Estimate)

and

mdl.MSE

.

Do you have any idea, why?

Here is my whole illustratory code:

tr_x = rand([10, 2]);
tr_y = rand([10, 1]);

get_MSE = @(mdlfun, tr_x, tr_y, b) mean((tr_y-mdlfun(b, tr_x)).^2);

modelfun = @(b, tr_x) b(1)*tr_x(:, 1).*sin(b(2)*tr_x(:,2));

mdl = fitnlm(tr_x, tr_y, modelfun, [1 1]);

disp(mdl.MSE);
beta = mdl.Coefficients.Estimate;
disp(get_MSE(modelfun, tr_x, tr_y, beta));

Thanks in advance, best,

PL