When a model starts, the equations are assembled into the main differential equation system. During the simulation, this DES is solved by one of the numerical methods built in AnyLogic. AnyLogic provides a set of numerical methods for solving ordinal differential equations (ODE), algebraic-differential equations (DAE), or algebraic equations (NAE).
You can change numerical methods used for solving equations in the System Dynamics solver section of the model’s Properties view.
- Differential equations — method used to solve ordinary differential equations (Euler and RK 4 are available).
- Algebraic equations — method used to solve algebraic equations (Modified Newton, Fast Newton, Classical Newton).
- Mixed equations — method used to solve algebraic-differential equations (RK45 Newton, Euler Newton).
There you can also configure numerical methods used for solving equations:
- Absolute accuracy — the desired absolute value accuracy for solving equations. Absolute accuracy is used when it is impossible to use relative accuracy — e.g., when the value is close to zero.
- Relative accuracy — the desired relative value accuracy for solving equations with methods that change the integration step (e.g. Newton). Used by default.
- Time accuracy — the desired time accuracy for finding change events (switch points) when solving equations.
- Fixed time step — fixed time step for methods using the fixed integration step (e.g. RK4).
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