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Purpose
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This demonstration case can be used to study the advection of a patch of ice in a bi-periodic channel
with a slab ocean (i.e. 1 ocean layer) and an agrif zoom in the center

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Experiments
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Two experiments can be configured:

a) A simple channel at 3km horizontal resolution (slightly variable => +- 10%)
              ==> in MY_SRC/usrdef_hgr.F90, uncomment the part "variable scale factors" and comment part "constant scale factors"

b) A simple channel at 3km horizontal resolution (constant scale factors)
              ==> in MY_SRC/usrdef_hgr.F90, comment the part "variable scale factors" and uncomment part "constant scale factors"

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How to run
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a) Compile and run the model once to get a mesh_mask.nc file with the following command:
../../../makenemo -r ICE_AGRIF -n ICE_AGRIF -m X64_ADA -j 4
mpirun ./nemo -np 1

b) Create the initial condition file for sea-ice (initice.nc) by running this python script: 
python ./make_INITICE.py

c) Run the model a second time
mpirun ./nemo -np 4

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What to look at
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the advection through an agrif zoom 1:3
   for a square (ice concentration) or a gaussian (ice volume)
      with either a constant velocity (ln_dynADV2D=T and define rn_uice & rn_vice)
               or a constant ice-atm. stress, thus velocity is calculated by rheology (ln_dynRHGADV=T)
      with 1 or 5 ice categories (jpl=1 or 5)
         (note that ln_dynADV2D=T only works with jpl=1)