FGH1D runs under the Windows operating system and was written in Visual Basic. The computationally expensive part is the diagonalization of a matrix, for which FGH1D uses the routines given in Numerical Recipes (Numerical Recipes. The Art of Scientific Computing. W. H. Press, S. A. Teukolsky, B. P. Flannery, W. T. Vettering, 1986 Cambridge University Press, Cambridge.)