The solver tab lets you choose which Ordinary Differential Equation (ODE) solver is to be used in the simulation. A list and short description of available solvers can be found in ODE solver reference.

**Absolute tolerance** - Absolute error tolerances that apply to the individual components of the solution vector. Absolute tolerance is a threshold value below which the value of the solution component is unimportant. The absolute error tolerances determine the accuracy when the solution approaches zero. The setting is globally defined in the solver tab but can be overridden if defined explicitly in a compartment.

*Default value = auto*

**Allowed step size violations** - Number of step size violations before displaying warning messages.

*Default value = 1*

**Enable saturation** – When saturation is enabled, non-negativeness in Compartments are imposed. If imposed and non-negative is defined in the Compartment the inventory cannot be negative.

*Default value = disabled*

**Fixed-step size (fundamental sample time)** - Step size for the fixed-step solver. The default is one-fiftieth of the simulation interval.

*Default value = auto*

**Initial step size** - Suggested initial step size. Initial step size sets an upper bound on the magnitude of the first step size the solver tries. If you do not set Initial step size, the initial step size is based on the slope of the solution at the initial time, and if the slope of all solution components is zero, the procedure might try a step size that is much too large. If you know this is happening or you want to be sure that the solver resolves important behaviour at the start of the integration, help the code start by providing a suitable Initial step size.

*Default value = auto*

**Limit data points to last** - Maximum number of data-points to store at workspace variables.

*Default value = 1000*

**LU decomposition matrix format** - Data format while solving the LU-decomposition.

*Alternatives = Auto, Dense and Sparse*

*Default value = Dense*

**Max order** - Maximum order formula used to compute the solution.

*Default value = 5*

**Max step size** - Maximum step size for variable-step solver. The default is one-fiftieth of the simulation interval.

*Default value = auto*

**Min step size** - Minimum step size for variable-step solver.

*Default value = auto*

**Norm control** - Control the error relative to the norm of the solution.

*Default value = disabled*

**Refine** - Increases the number of output points by a factor of Refine. If Refine is 1, the solver returns solutions only at the end of each time step. If Refine is n >1, the solver subdivides each time step into n smaller intervals and returns solutions at each time point. The extra values produced for Refine are computed by means of continuous extension formulas. These are specialized formulas used by the ODE solvers to obtain accurate solutions between computed time steps without significant increase in computation time.

*Default value = 1*

**Relative tolerance** - Relative error tolerance that applies to all components of the solution vector y. This tolerance is a measure of the error relative to the size of each solution component. Roughly, it controls the number of correct digits in all solution components, except those smaller than thresholds defined in Absolute tolerance. The default, 1e-3, corresponds to 0.1% accuracy.

*Default value = 0.0010*