Enabling support for GNU Octave within the FOCUS software package

FOCUS, the “Fast Object-Oriented C++ Simulator” (https://www.egr.msu.edu/∼fultras-web/), is a free software package that enables rapid calculations of continuous-wave and transient pressure fields generated by single transducers and phased arrays. Pressure field calculations in FOCUS converge quickly and achieve very short computation times through linear memory-efficient calculations that employ the fast nearfield method. This capability extends to fast and accurate biomedical ultrasound simulations within FOCUS. Moreover, FOCUS supports nonlinear pressure field calculations with the continuous-wave and transient Khokhlov-Zabolotskaya-Kuznetsov (KZK) equations for circular and spherical transducers. Additionally, the Angular Spectrum Approach (ASA), a frequency domain solution to linear computational methods that is ideal for large volumetric pressure field computations, is also included within the FOCUS package. Initial success with MATLAB motivates the creation of an Octave version that replicates the core functionalities of the original FOCUS package. Octave is similar to MATLAB, but unlike MATLAB, Octave is free software. Building and compiling FOCUS in Octave involved minor alterations due to discrepancies in syntax and function calls. Compiling MEX files in Octave simplified the conversion process while introducing additional memory overhead compared to rewriting C++ code for Oct-file structuring. The performance and capabilities of FOCUS in Octave are demonstrated and discussed.