[Physics] Les Houches Accord PDF Interface

 LHAPDF provides a unified and easy to use interface to modern PDF sets. It is
 designed to work not only with individual PDF sets but also with the more
 recent multiple "error" sets. It can be viewed as the successor to PDFLIB,
 incorporating many of the older sets found in the latter, including pion and
 photon PDFs. In LHAPDF the computer code and input parameters/grids are
 separated thus allowing more easy updating and no limit to the expansion
 possibilities.