I\'ve reduced my problem (table layout algorithm) to the following problem:
Imagine I have N variables X1, X2, ..., XN. I also have some
What you have there is a pretty basic Linear Programming problem. You want to maximize the equation X_1 + ... + X_n
subject to
X_1 >= 2
X_2 + X_3 >= 13
etc.
There are numerous algorithms to solve this type of problem. The most well known is the Simplex algorithm which will solve your equation (with certain caveats) quite efficiently in the average case, although there exist LP problems for which the Simplex algorithm will require exponentially many steps to solve (in the problem size).
Various implementations of LP solvers exist. For example LP_Solve should satisfy most of your requirements