This is the v.3.1.3, codenamed Big Smoke, release of gprMax. Version 3.1.3 contains general usability and performance improvements, as well as the following specific enhancements and bug fixes since v.3.1.2: Speed up for writing geometry files (pull request #138 ) Tweaks to improve calculation of maximum frequency of interest used in dispersion analysis (this is used as a guidance for users) Added extra error messages to check when rough surface trough/peaks do not correspond to dimensions of fractal box that they are associated with. Clean/tidy of MPI task farming code - added an alternate MPI implementation that can be used in circumstances where MPI.Spawn method is not supported. This can be accessed via the command line flag -mpialt and requires gprMax to be run using the style mpiexec -np X where X is the number of model runs + 1 (for the master task) Changed ID of material created for resistive voltage source - now uses voltage source position in ID rather than conductivity value which could be the same for multiple sources. Fixed bug introduced with changes to interpolation of imported waveform (bug #139 ) Added code to speed up the building of cylinders that are aligned to a grid axis. v.3.1 continues our whisky-based naming, and is also a reference to the cities of Edinburgh (Scotland) and San Francisco (USA). Why? Because the development of v.3.1 was funded, through a research project, by Google. The most significant feature of this release is the ability for simulations to utilise general-purpose computing using graphics processing units (GPGPU). We have used NVIDIA's Compute-Unified Device Architecture (CUDA). Our testing on both consumer and data centre NVIDIA GPU cards has shown dramatic performance increases over our parallelised CPU (OpenMP) implementation. You can read about how to use the GPU functionality and find all the features of gprMax described in detail in the User Guide (http://docs.gprmax.com) Please report any bugs with code via Issues on GitHub. For general help and questions about using gprMax visit our Google Group forum (http://www.gprmax.com/forum.shtml)