# Comparing DRS

Discrete rate simulation combines the event-based timing of discrete event simulation and the continuous variables calculations found in continuous simulation. It predicts and schedules events when the system needs to calculate a new set of rates and determines the appropriate rate of flow for each branch or stream.

Discrete rate simulation is similar to discrete event simulation in that both methodologies model the operation of the system as a discrete sequence of events in time. However, while discrete event simulation assumes there is no change in the system between consecutive events, in a discrete rate simulation model the flow continues to move at a constant rate such that, for example, the level in a tank could change. Another difference is that discrete event simulation models are overwhelmingly concerned with the status of system entities (discrete objects moving through the system) while discrete rate simulation models are concerned with the status (quantity and location) of homogeneous flow. For rate-based systems, discrete rate simulation has faster computational times and is more accurate in calculating mass balance compared to discrete event simulation.

Discrete rate simulation is also similar to continuous simulation in that it simulates homogeneous flow. In addition, both methods recalculate flow rates, which are continuous variables, whenever a state change occurs. However, discrete rate simulation S differs from continuous simulation in that it is event-based and does not simulate every time slice. Modeling linear flow systems using continuous simulation has limitations because it usually is unable to detect important events, such as a tank becoming full or empty, until after the event has occurred plus requires many more system recalculations during the course of the simulation.

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