Constraint graph (layout)

In some tasks of integrated circuit layout design a necessity arises to optimize placement of non-overlapping objects in the plane. In general this problem is extremely hard, and to tackle it with computer algorithms, certain assumptions are made about admissible placements and about operations allowed in placement modifications. Constraint graphs capture the restrictions of relative movements of the objects placed in the plane. These graphs, while sharing common idea, have different definition, depending on a particular design task or its model.