In reply to Adelyn.

Are you able to use the equation to solve for the variable you want in terms of the other variables? SAS/IML has routines for numerical derivatives, but you need to have the equation in the form y = f(x1,x2,...,x8). If you are having problems algebraically inverting an equation, you might try a symbolic algebra package, such as Mathematica. I suggest you post a question to the SAS Support Communities at https://communities.sas.com/ and supply for details about your problem. Choose the "SAS/IML Software and Matrix Computations" board.