Copyright (C) 2001 Michel Juillard

 GCOMPARE : GCOMPARE ( [ 'file1' ; 'file2' ] , [ 'var1' ; 'var2' ...] ) 
  This optional command plots the trajectories of a list of
  variables in two different simulations. One plot is drawn
  for each variable. The trajectories must have been previously
  saved by the instruction DYNASAVE. The simulation in file1
  is refered to as the base simulation.