MATLAB: What is xout variable

MATLABsimulinkxout

After simulation, variable which is named 'xout' is spawned. It is very big size matrix, so I would like not to make it.

[Updated 1]

xout is the logged data variable contains state value of the model.

Maybe I don't understand correctly: if you want to set all negative entries of fval to 0 you can add

fval(fval < 0) = 0;

at the end of your function. Otherwise follow Walter answer.

If your input is x^2 + 2 + x then you cannot isolate x to one side of an equation, as your input is not an equation.

If your input is implicitly x^2 + 2 + x = 0 then your example output of x = x^2 + 2 is incorrect: instead x = -x^2 - 2

You cannot always isolate one variable -- not unless you are willing to make some restrictions on the form of the equation.

If you have a polynomial as input, then

S = x^2+2+x;
c = sym2poly(S);
isolated_x = x * c(end-1) - S;