Boundary conditions

The boundary conditions are usually dealt with using one or more ghost cells, in our Fortran case these are cells 0 and meshmax+1. Before the integration step the value for W is set in a pre-determined way, depending on the problem. Possible choices are:

• Inflow: The ghost cells are filled with the material flowing onto the grid.
• Outflow: The ghost cells are filled so that material can flow off the grid without influencing the material on the grid (normally achieved by setting W equal to the value of the last proper grid cell).
• Reflection: The ghost cells are filled so that it seems that the material runs into a wall (normally achieved by setting W equal to the value of the last proper grid cell but changing the sign of the velocity).