Abstract
Qualitative simulation is a well-known reasoning technique that involves the use of simulation technologies. Reasoning is made to determine qualitative values and change directions of system variables, and it is done for each time point and time interval following the time point. Qualitative variables possess continuous qualitative value sets that are discretized by landmark points. Qualitative simulation uses qualitative time representation and its quantitative value is of no interest. The main purpose of this study was to develop a technique to determine time steps for a quantitative simulation under guidance of qualitative information. The proposed technique determined time advances using qualitative and quantitative information together to obtain a robust time step as wide as possible for simulation time advances. For this purpose, sign algebraic properties and derivation roots of quantitative equations and qualitative variable values with their change directions were used to compute time advances. In the approach, qualitative simulation determined landmark points to be advanced, and quantitative simulation calculated the duration required. Using the proposed algorithm, the simulation is advanced instead of iterating simulation time for a predefined time step and checking whether or not there is any activity in the interval, directly to the time points that are qualitatively different.
Highlights
Qualitative simulation (QS) is defined as a reasoning technique using simulation, and it generates possible value and their change directions that are defined as state on time axis for continuous event systems, using qualitative information of the system being simulated, and the states following each other in time point and time interval sequences constitute behavior trees [1, 2]
Qualitative differential equations (QDEs) utilized by QS represent a function family, not a specific function; they accommodate a set of functions beneath
The main motivation of this study is to develop a simulation time management technique that advances simulation steps to system discontinuity points that are discovered by qualitative reasoning and sign algebra
Summary
Qualitative simulation (QS) is defined as a reasoning technique using simulation, and it generates possible value and their change directions that are defined as state on time axis for continuous event systems, using qualitative information of the system being simulated, and the states following each other in time point and time interval sequences constitute behavior trees [1, 2]. Function dependent main idea is to calculate a time step as wide as possible to reach the qualitative state vector point (named as landmark points) that is close to the current state value of simulation model depending on its change in direction instead of reaching the qualitative value by many small time steps that the quantitative equations are solved for. In some sense, this involves mapping a continuous space into a discrete one and allowing it to reach a state point directly, instead of traversing from one state to another by small time steps. Advantages and disadvantages of the proposed solution are discussed
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