[zbyszek]

As far as I recall, QCD gives you a nice simple formula - a path integral over quantum operators - for any quantity you want. Lattice QCD works out the answer with great big Monte-Carlo integration. The tricky bit is defining a field theory on a finite discrete space-time lattice that is provably equivalent to the continuum theory after controlled extrapolations to the continuum. And you have to show that you can define the correct operators in the lattice theory that really do give the quantities you want. Then you need to implement this in code that runs blazingly fast over huge data sets. These considerations, and the fact that there are all sorts of solutions to these problems which might supported by a code base, tend to make code implementations complicated.