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, for example, when the value is close to zero.
• Time accuracy — The desired relative time accuracy for finding change events (switch points) when solving equations, i.e. to better adjust the fixed integration step to the discrete events (for System Dynamics models that have discrete events).
• Relative accuracy — The desired relative value accuracy for solving algebraic and mixed equations with methods that change the iteration step (e.g. Newton).
• Fixed time step — The fixed time step for methods using the fixed integration step to solve differential and mixed equations (e.g. Euler, RK4).

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