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).