but i mention again that my final equation doesnt contain any of those symbolic var
But your final F is generated from calculations with these variables, so they inherit their symbolic type. At no point in your code, do you do anything to convert from symbolic to double. When I run your function on some sample input, I obtain
So, as you can see, your output is still of type sym.
but i remove them after some calculations with "collect" and "coeffs" commend
Nope. The output of these commands are still of type sym. I explained to you here (and you thanked me emphatically) that the commmand double() was the way to convert from sym to double.