The LPCVD Furnace Model uses the Twopnt package to solve the discrete equations described above. Twopnt is documented in a separate manual, so we only include a brief description here. Twopnt uses Newton's method to find a steady-state solution. If this is not immediately successful, it uses time integration to find good guesses from which to begin Newton's iteration. Finding a solution may involve a number of iterations between the two methods.

The Twopnt program has controlling parameters that can be varied to obtain solutions more quickly or to improve convergence behavior. A complete description of these parameters, and recommendations for setting them, can be found in the Twopnt manual. The LPCVD Furnace Model supplies defaults that have been found effective for these systems. Solve the Problem lists the relevant Twopnt controlling parameters along with the LPCVD Furnace Model default values and the keywords that change them. Changes to Twopnt 's parameters remain in effect for subsequent simulations run from a given input file unless they are changed again. RESET THE DEFAULTS undoes any changes to the LPCVD Furnace Model's choices. When the LPCVD Furnace Model begins, it always assumes its default choices when more than one model is being run sequentially. The files that store reactor model solutions do not store the values of the Twopnt controlling parameters.