Remarks

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Remarks

# Note 1: ghost cells - (halos)

A cell (real cell) is an elementary mesh element of the spatial discretisation of the calculation domain. The mesh is made of ncel cells. When using periodicity and parallelism, extra `ghost'' cells (called`halo'' cells) are defined for temporary storage of some information (on a given processor). The total number of real and ghost cells is ncelet.

- Indeed, when periodicity is enabled, the cells with periodic faces do not have any real neighbouring cell across these particular faces. Their neighbouring cell is elsewhere in the calculation domain (its position is determined by the periodicity). In order to temporarily store the information coming from this `distant'' neighbouring cell, a ghost cell (`halo'') is created.
- The same kind of problem exists in the case of a calculation on parallel machines: due to the decomposition of the calculation domain, some cells no longer have access to all their neighbouring cells, some of them being treated by another processor. The creation of ghost cells allows to temporarily store the information coming from real neighbouring cells treated by other processors. The variables are generally arrays of size ncelet (number of real and fictitious cells). The calculations (loops) are made on ncel cells (only the real cells, the fictitious cells are only used to store information).

# Note 2: internal faces

An internal face is an inferface shared by two cells (real or ghost ones) of the mesh. A boundary face is a face which has only one real neighbouring cell. In the case of periodic calculations, a periodic face is an internal face. In the case of parallel running calculations, the faces situated at the boundary of a partition may be internal faces or boundary faces (of the whole mesh);

# Note 3: faces-nodes connectivity

The faces - nodes connectivity is stored by means of four integer arrays: ipnfac and nodfac for the internal faces, ipnfbr and nodfbr for the boundary faces. nodfac (size lndfac) contains the list of all the nodes of all the internal faces; first the nodes of the first face, then the nodes of the second face, and so on. ipnfac (size: nfac+1) gives the position ipnfac(ifac) in nodfac of the first node of each internal face ifac. Therefore, the reference numbers of all the nodes of the internal face ifac are: nodfac(ipnfac(ifac)), nodfac(ipnfac(ifac)+1), ..., nodfac(ipnfac(ifac+1)-1). In order for this last formula to be valid even for ifac=nfac, ipnfac is of size nfac+1 and ipnfac(nfac+1) is equal to lndfac+1. The composition of the arrays nodfbr and ipnfbr is similar.

# Note 4: modules

The user will not modify the existing modules. This would require the recompilation of the complete version, operation which is not allowed in standard use.