Tool to obtain the cluster density parametrisation for simulation 
(as input for PrimaryIonisationProcessor) for different gas mixtures

requires ILCSOFT and Garfield (http://svn.cern.ch/guest/garfield) with Heed

How to use:
===========
- set the necessary environment variables, i.e. init ILCSOFT and
  export GARFIELD_HOME="path/to/garfield"
  export HEED_DATABASE="$GARFIELD_HOME/Heed/heed++/database"

- edit nclusters_momentum.C to add your gas mixture

- make

- ./nclusters_momentum <chosen-gas-number>
  this gets the cluster density vs momentum/mass for the chosen gas

- run parametrise.C on the created output file (either compiled or in CINT)
  check that the fit output looks reasonable

- rename the created heedparameters.dat to a name describing your gas mixture
  and use as ClusterDensityFile in PrimaryIonisationProcessor