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HOPPET: Higher Order Perturbative Parton Evolution Toolkit
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HOPPET is a Fortran 95 package for carrying out DGLAP evolution and
other common manipulations of parton distribution functions (PDFs).

Within HOPPET, PDFs are represented on a grid in x-space so as to
avoid limitations on the functional form of input
distributions. Decent speed and accuracy are obtained through the
representation of splitting functions in terms of their convolution
with a set of piecewise polynomial basis functions, and Runge-Kutta
techniques are used for the evolution in Q.

Unpolarised evolution is provided in the MSbar scheme to NNLO in the
coupling, including heavy-quark thresholds, and polarised evolution to
NLO. The code is structured so as to provide simple access to the
objects representing splitting function and PDFs, making it possible
for a user to extend the facilities already provided.

The latest version can always be obtained from

    svn checkout http://svn.hepforge.org/hoppet/trunk hoppet

Details of changes are to be found in the file ChangeLog, while
summaries of changes between releases are in ReleaseNotes.


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F95 compilers
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You will need a Fortran 95 compiler to compile this package. 

The gfortran compiler is widespread. Versions upwards of a recent 4.3
are OK. Older versions generate incorrect code for HOPPET and should
be avoided. The code is acceptably fast, though not quite as fast as
with commercial compilers.

The free g95 (www.g95.org) compiler is another option, though when
tested around 2008 its executables were fairly slow. It is easy to
install if you don't already have a recent version on your system.

The intel (ifort) compiler (versions 8.1.033 upwards) may still exist in a
semi-free version for non-commercial use under linux and produces fast
executables.

The release has also been tested with the lahey lf95 commercial
compiler, which also generates fast code.


Compilation
-----------
For details see the INSTALL file. To get moving quickly, just specify
an installation prefix and a fortran compiler (FC), and then do

  ./configure --prefix="..."  FC="..."
  make 
  make check
  make install      [if you're interested]
  make install-mod  [if you want the f90 module files installed too]

This is not autotools based: if you're used to more advanced usage of
autotools scripts, you'll be disappointed here...

Example programs
----------------

The main example program is examples_f90/tabulation_example.f90

An equivalent program with the startup, pdf initialisation and
evolution spread across different subroutines is given as
tabulation_example_2.

An equivalent program based on the streamlined interface is given as
tabulation_example_streamlined.

Compiling f77 example programs (examples_f77) using g77 is a little
trickier because of the need to include the correct f95
libraries. Look inside the suppplied Makefile and if need be edit it
manually.

     cd ../example_f77
     # <edit the Makefile directly>
     # compile
     make tabulation_example
     # run the program should give output identical to that from
     # example_f90/tabulation_example
     ./tabulation_example

In the same directory there is a C++ example

     make cpp_tabulation_example
     ./cpp_tabulation_example

which again does the same things (though in this case it uses the
simpler of the two vanilla initialization calls).

Other programs provided in the example_f77/ directory illustrate the
use of the vanilla interface in conjunction with LHAPDF
(compare_lhapdf_hoppet.f), and show how use the feature of getting
convolutions with splitting functions (convolution_example.f).

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Documentation
-------------

Detailed documentation is available as doc/HOPPET-v1-doc.tex .


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Benchmarking
------------

The benchmarking/ directory contains the programs used for the full
benchmarking, accuracy and precision testing. 


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Compiler warnings
-----------------

When the hoppet library is being built, on some systems the following
warnings may be reported 

  /usr/bin/ranlib: file: libhoppet_v1.a(hoppet_v1.o) has no symbols
  /usr/bin/ranlib: file: libhoppet_v1.a(types.o) has no symbols
  
  ranlib: file: libhoppet_v1.a(hoppet_v1.o) has no symbols
  ranlib: file: libhoppet_v1.a(types.o) has no symbols

These warnings do not indicate an actual problem. They are simply a
consequence of the fact that some of the source (.f90) files contain
only information about interfaces and constants, so that the resulting
object (.o) files are essentially empty.