The most part of the program is spent manipulating **ScalarField** instances. A scalar field is basically a 3D field of continuous floating point data organized on a grid with as `[nr radial][ni layer][ns sector]` (if we use $`nr*ni*ns`$ grids) dispatched other an MPI communicator. 2D fields are just flat 3D fields ($`ni \equal 1`$).
This object store the data as a [std::valarray<double>](http://www.cplusplus.com/reference/valarray/) object field, but also export it as an old fashioned C pointer[^3].
**ScalarField** are use to represent any kind of gas properties like density, energy, temperature etc..
The disk geometry and physic configuration are described through a set of classes that are almost (almost) a [Singleton](https://en.wikipedia.org/wiki/Singleton_pattern)(because we do not need many of them). All object that need to have access to those information do so by referencing the appropriate instances.
