1. compute initial volume via the PolygonGeometricalPropertis
2. compute the volume in every cell (No Dirichlet BC) with source term
and flow rate
3. now the file writer has an open text method, a write text method and
a close text method
-> WRITE FILE TEXT:
Write solution for every time step, in a new format. The file name is
DecimalFormat.

-> COMPUTE WATER VOLUME:
In a close system, it's computed the water volume at every time step so
it can be possible to verify the model conservation of the mass

-> SIDES IN BASE 1
The code is modified so the input array Ml is read in base 1, but all
the calculations are in base 0