The derivative of sex can be expressed as a linear function reflected across the X-Axis. Depending upon the participants (and their skill), it could be any variation of the following expression:
Y` = -X
That's what it should be, anyway. An unforunate (and often embarassing) scenario is when one member of the party is somehow incompatible, resulting in a warping of the original F(X) equation into something other than a concave-up parabolla. In this case, the sex derivative may appear as a sheepish horizontal line at Y = .

Don't let this happen to you. Make sure your sex is both inverted and exponential.