AngstromCube

This README is only about the code base, please refer to ../README.md for the entire application

The AngstromCube code base is structured as follows: There is at most one namespace per file. Each namespace offers the function

    status_t all_tests(int const echo=1);

and should be listed in a43_main.cxx to be envoked via the command line option -t or --test. The executable shows a simple help when called with -h or --help.

Output to stdout should always depend on the echo-levels so it can be turned off completely. Warnings printed to stdout, to stderr, are recorded in memory and summarized at the programs end.

All log output to stdout should start a line with # and, if the information is about a specific atom, followed by some atom identifier label.

For development it is sometimes helpful to have plotable output. Here are two options:

1. Use the helper functions dump_to_file offered by debug_output.hxx
2. Print to stdout directly in the format x y0 y1 y2 ... yn without # in front The latter can easily be plotted e.g. by the xmgrace -nxy tool. For clarity, prepend a line with ## x_legend y_legends :, mind the double hashtag! When plotting an entire log file grep \#\# <logfile> can then help to identify graphs.

When including functionality from another header file (self-written onces or libraries), the coder is encouraged to keep a list of symbols up to date, listing only those symbols that appear in the current source file, e.g.

    #include "debug_output.hxx" // dump_to_file
    #include "debug_tools.hxx" // ::read_from_file

The syntax ::read_from_file indicates that there is a namespace in front which should match with the filename of the header file, i.e. debug_tools in this example. This convention is inspired by the use , only: syntax of Fortran90.

Macros and Preprocessor symbols The most important preprocessor symbol is

  #ifdef DEVEL
  // code that is useful during development but should not appear in release versions
  #endif

The cppp -U DEVEL tool is used to remove all DEVEL-code from the code base while maintaining the other macros. Here, -U stands for undefine. Please try to keep the release code base small and readable! The cppp-tools is avialable at https://github.com/BR903/cppp

You can write Fortran in any language The saying above moques about the bad programming style many Fortran programs are written in. However, there are some nice things in Fortran90 that come handy so they were re-introduced into the C++ of this project:

    vec(:) = b(:)

However, to keep it as basic as possible, it can be done by

    #include "inline_math.hxx" // set
    set(vec, n, b);

but we have to know the length of the arrays. Certainly, set is templated, so where x and b are pointers, not necessarily of the same type. set also supports scaling by and assignment of a scalar value

    set(vec, n, vector, scalar_factor);
    set(vec, n, scalar_value);

More vector functionality can be found in inline_math.hxx as e.g.

    scale(vec, n, scalar_value);
    scale(vec, n, vector[, scalar_factor]);
    product(vec, n, vector, vector_factors [, vector_factors][, scalar_factor]);
    add_product(vec, n, vector, scalar_factor);
    add_product(vec, n, vector, vector_factors[, scalar_factor]);

The largest feature-envy for Fortran90, however, are the intrinsic support of multi-dimensional arrays including run-time checking of index-out-of-bounds. Please see data_view.md for more details.

Style Comment In each code file (*.hxx, *.cxx) we try to make dependencies easily identifiable. In Fortran, this would be a "use , only: , " statement. In C++ we treat it as a comment after the included header file #include // std::printf, ::snprintf #include "tools.hxx" // ::foo, ::bar We only mention the namespace name when it deviates from the header's file name, e.g. std:: should be mentioned once here.

Green function code

Compilation

./green can be compiled for the CPU without CUDA to check its functionality.
Activate -DHAS_NO_CUDA in Makefile.green
Otherwise, green is a CUDA code for NVIDIA GPUs.
Please use either Makefile.green in this folder or CMake

Input

./green expects `Hmt.xml`, an XML-formatted ASCII file containing
the local and non-local parts of the potential operator as
exported by write_to_file in `include/grid_operators.hxx`

Dependencies

./green needs the header-only library rapidxml.
./green can include the header-only library tfQMRgpu.