Google for a class in (classical) control theory. This is a standard topic for electrical, mechanical, and chemical engineering programs. For implementing a PI

Google for a class in (classical) control theory. This is a standard topic for electrical, mechanical, and chemical engineering programs. For implementing a PID loop, you can do it in pretty much any language you want -- it's relatively straightforward once you know the math. You can even do it in hardware via an analog circuit if you desire. However MATLAB / Simulink are commonly used when experimenting with system parameters due to the presence of straightforward plotting tools and numerical ODE solvers.