Use of simulation programs for the modelling of the Next Linear Collider

The Next Linear Collider is an electron-positron accelerator unprecedented in its size, energy, and tight tolerances. We describe the suite of simulation tools which are widely used in designing and modelling the performance of the NLC. In order to achieve a uniform beamline description and permit simulation of all facets of the collider, an extended version of the Standard Input Format (xSIF) has been developed and implemented in MAD and DIMAD. We discuss several enhancements to the MAD and DIMAD calculation engines necessary to properly simulate the most challenging regions of the facility. We also describe enhancements to LIAR which allow it to be used as the tracking engine for a tuning/feedback simulation written in MATLAB. Finally, we discuss the additional software needed to model the beam stabilization and tuning processes.