The window for basic ODE control and status is shown below. The choices of user level are Basic and Advanced . If the basic level is chosen, only the parameters shown in the upper box of the window need to be set. The stiffness of the model equations is the major consideration when choosing the solver to use. If the ratio is between 2 and 10, the equations are mildly-stiff.
Error tolerances Both relative and absolute error tolerances for the error tests can be specified.
Note that when any dynamic variable has an initial condition of zero or passes through zero at any later value of the independent variable, it is important to set the absolute tolerance to a non-zero value. Otherwise, the step will have zero overall tolerance, and the solver will remain at that value of the independent variable indefinitely. Thus, the absolute error tolerance should be set to a non-zero value when the absolute noise of the solution or when any of the solution values are may have a zero value. The total number of times the ODE function was evaluated during the current simulation time step. For the current simulation time step, the number of steps that were accepted by the ODE solver based on the error tolerances set for the simulation run.