Seems to me that you already have a function. Whether it is positive or not depends on the parameters you feed it.i would like to derive a simple positive function from the following
Y=-2x-4.2y-6.1z-7.5t-9.3q
Or maybe zero. It definitely won't be negative.The function Y squared will be everywhere posive in R5(5-space). I'm assuming tha small-y and big-Y are different.