1. A computer-implemented method of determining a flow, comprising: receiving, using one or more data processors, flow data identifying inflow and outflow relationships among a plurality of entities, wherein each inflow and outflow relationship has an associated flow proportion, and wherein each inflow and outflow relationship represents how money flows in an enterprise; receiving, using the one or more data processors, source-entity data identifying one or more source entities that contribute, wherein the source-entity data includes an associated contribution amount, and wherein each source-entity has one or more outflow relationships associated with one or more other entities; receiving, using the one or more data processors, target-entity data identifying one or more target entities, wherein each target-entity has one or more inflow relationships and one or more outflow relationships associated with one or more other entities; generating, using the one or more data processors, a model corresponding to a system of linear equations, wherein the model is generated using the flow data, the source-entity data, the target-entity data, the flow proportions, and the contribution amounts; generating, using the one or more data processors, a revised model corresponding to a modified system of linear equations, wherein the revised model is generated by removing flow proportions associated with all outflow relationships of the one or more target-entities; and determining, using the one or more data processors, a flow among the plurality of entities by solving the modified system of linear equations corresponding to the revised model.