Unless otherwise noted, This software is in the public domain because it contains materials that originally came from the United States Geological Survey, an agency of the United States Department of Interior. For more information, see the official USGS copyright policy at http://www.usgs.gov/visual-id/credit_usgs.html#copyright
This software contains two source files obtained from the Netlib repository (http://www.netlib.org/). These files are named calerf.f and derfc.f and implement an approximation to the error function. The contents of these files have been copied from the Netlib at http://www.netlib.org/specfun/erf (accessed 22 March 2016). As stated in the Netlib's FAQ page at (http://www.netlib.org/misc/faq.html, accessed 22 March 2016) "The Netlib repository contains freely available software, documents, and databases of interest to the numerical, scientific computing, and other communities. The repository is maintained by AT&T Bell Laboratories, the University of Tennessee and Oak Ridge National Laboratory, and by colleagues world-wide. The collection is replicated at several sites around the world, automatically synchronized, to provide reliable and network efficient service to the global community."
The source code can be compiled using freely available gfortran (http://gcc.gnu.org/fortran/) or any of the commercially available Fortran compilers that support Fortran 95 and Fortran 77. Sample make files are included, but they might require editing in order to work on specific platforms.