Theory is the mathematical work. Sometimes it may be derived out of an observation from the experiments and at other times, it can be a point of start and then the formula are checked with experiments and seen if they are in agreement. Computation, however, is running a simulation of the theory on a computer to see what data can be derived. Initially the data is derived for known parameters to see if the experimental and simulation results are in agreement, if the model works, further properties may be derived. The difference between two is a thin line. I can think of simulation as a direct application of theory.