cp2k/tools/Fun2D

A package to generate Fortran code for the evaluation of bivariate functions.
Using recursive bisection and lagrane interpolation at padua points, the code
and necessary tables are being constructed.

The function (f) must be defined in drvrec_mpfr.f90,
and its domain must be (transformed to) rectangular.

The settings for the bisection, accuracy, ... are set in recurse.f90. Most important
are the degree of the interpolation, and the target error.
The actual error is usually smaller than the estimate of the error.
The degree of the interpolation and the target error influence the size of the tables,
and speed of evaluation.

The code is interfaced to the arbitrary precision library MPFR, with a convenient Fortran
wrapper. However, as long as derived type finalization (a Fortran2003 feature) is not available,
memory is not freed during MPFR math, and thus a significant amount of memory is needed. To reduce the
impact, drvrec_mpfr has been transformed into a little program, so that the OS frees the memory in between
calls.

The code for interpolation through the Padua points is based on an older version of Padua2D,
kindly made available by the authors (Marco Caliari and Marco Vianello and Stefano De Marchi)
see top of padua2_mpfr.f90 for further credits.