This is the documentation for the Fast Fourier Modal Method (FFMM) Python package. Our goal here is to develop the fastest and most accurate FMM algorithm for scientific resarch and industrial applications such as optical critical dimension metrology in semiconductormanufacturing, with the help of multi-core CPU and GPU computing. To achieve this, we will use the libraries and platforms such as MPI, OpenMP, and CUDA, which are widely used in scientific computing and provide efficient parallel computing capabilities.