1. A computer-implemented method for analyzing costs associated with a cost flow model that specifies relationships among a plurality of entities, wherein a relationship specifies a direction of a cost flow between entities in the cost flow model, said method comprising: receiving data associated with the cost flow model that identifies costs associated with the relationships among the plurality of entities; receiving source-entity set definition information which defines a set of source entities in the cost flow model that contribute money to entities in the cost flow model; receiving target-entity set definition information which defines a set of target entities in the cost flow model that receive money from entities in the cost flow model; generating a system of linear equations based upon the received data associated with the cost flow model and based upon the received source-entity set definition information and based upon the received target-entity set definition information; wherein data about relationships, which are associated with the set of target entities and which satisfy a relationship removal criteria, is not included in the generated system of linear equations; solving the system of linear equations in order to determine contribution values from the source entities to the target entities; whereby the determined contribution values are provided to a user or an external system.