FW2_5D: A MATLAB 2.5-D electrical resistivity modeling code

We present a 2.5-D forward modeling algorithm for electrical resistivity data. The algorithm incorporates a boundary condition and source singularity correction that greatly reduces the need to pad the model space. In addition, the algorithm includes an optimization method for estimating the appropriate Fourier coefficients to achieve an accurate 2.5-D approximation. The optimization scheme uses a gradient-based search to find the optimal coefficients. We compare results from our algorithm to two analytical solutions. We are able to achieve errors on the order 1% when compared to these models. We have implemented the algorithm as an open source MATLAB-based forward modeling package. The MATLAB code is useful for exploring subsurface current flow. It has been coded so that it can be easily ported to work with inversion routines. The code is computationally efficient and suitable for solving 2-D problems with a large number of model parameters.