= Compiling GiBUU =

Compiling GiBUU usually is as easy as typing '''make''' in the GiBUU base directory. However, a couple of options are available for special situations (see also [http://gibuu.physik.uni-giessen.de/Documentation/makefile_robodoc/masterindex.html Makefile Documentation]).

Before compiling, make sure that all [wiki:tools prerequisites] are fulfilled.

Note that the whole compilation process is steared by GNU make. GiBUU is always compiled statically, so that we get a monolithic executable which does not depend on system libraries (with the exception of Mac OS X where static linking is not supported).

== Choosing a Compiler ==

By default the Makefile uses the first supported compiler which is found on your system (ifort, gfortran, g95, sunf95 or pgf95 - in this order). But you can also tell the Makefile which compiler to use, by doing e.g.:

{{{
make FORT=gfortran
}}}

In this way you can also specify the exact path of the compiler explicitly:

{{{
make FORT=/opt/g95-install/bin/g95
}}}


== Choosing an Optimization Level ==

By default GiBUU is compiled with debugging flags, which is good for development and bug tracking, but the produced executable may be quite slow. If you want an optimized executable, you should compile with

{{{
make MODE=opt3
}}}

This works with all compilers and lets you specify the optimization level (0-3). Another option is to use profiling flags:

{{{
make MODE=prof
}}}

Currently this only works with ifort & gfortran, and produces an executable which is suitable for profiling with gprof.


== Floating Point Exceptions ==

Checks for floating point exceptions are turned off by default. To change this you can use e.g.

{{{
make FPE=0
}}}

This sets the level for floating point exceptions, which can be 0-3, where FPE=3 means none and FPE=0 means all. FPE=3 is the default. This flag is only supported with ifort and gfortran. Note: We recommend not to use FPE, unless you feel really adventurous. The resulting executable is likely to crash (in particular, PYTHIA has trouble with FPE).


== Parallel Make ==

If you have a multi-core machine, you can speed up the compilation process by specifying the number of cores to be used by make. E.g. on a quad-code machine you could do

{{{
make -j4
}}}

This can potentially be up to four times faster than the standard single-threaded make ("-j1"), since four files can be compiled in parallel.

== Rebuilding from scratch ==

If you want to discard all the object files which have already been generated (e.g. to rebuild with a different compiler or different options, or after making major changes to the code), you should type

{{{
make renew
}}}

This will clean up all present object and module files and rebuild the dependencies, giving you a fresh start in building GiBUU.