Multi-dimensional bin packing in general does not have PTASes. However, for the constrained versions of the problem used in practice, PTASes and other tractable

Multi-dimensional bin packing in general does not have PTASes. However, for the constrained versions of the problem used in practice, PTASes and other tractable algorithms exist. Same with the STP - very difficult in non-Euclidean space, but all practical applications are in Euclidean spaces.