dsm.f90: A computer code for the solution of an inverse problem of ground water hydrology by the differential system method

The identification of the transmissivity, T, of a confined aquifer, for which the 2D flow condition holds, can be obtained with the differential system method when several sets of data are available. If we consider stationary flow conditions, the necessary data are at least two couples of piezometric heads and source terms such that the two hydraulic gradients are not parallel at any point, and the value of T at one point only. The method has been implemented in the computer code dsm.f90, developed with the FORTRAN 90 programming language. The computer code allows the user to input several sets of data, an initial estimate of the T field or alternatively several starting points for the integration of the differential system. Moreover, the code performs several checks to identify the T field in a robust way and to avoid unphysical results, e.g. negative or very large values of T.