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Boundary conditions

You have to specify all boundaries, even for 1D/2D simulations, although only the necessary will be applied. Zero gradients copies the last boundary cell values into ghost cells, reflecting boundaries are self-explaining and small padding means $1E-50$ values, i.e. small, are copied in the ghost cells. Inflow and Outflow boundary conditions are explained in detail in the chapter about boundary conditions. Periodic boundaries are needed often for test scenarios (e.g. Kelvin Helmholtz instability tests.)
In Fig. 1.1 the orientation of the boundaries in space is given. Note that in the case of 1D/2D simulations the boundaries for the unused axes do not have any effect, but must still be present in the parameterfile.

Figure 1.1: TYCHO's boundaries orientated in space.

#Boundary conditions
#Boundary conditions gradient
#2.....small padding
#3.....outflow boundaries
#4.....inflow boundaries
#5.....periodic boundaries
#bound.down, bound.up,bound.left, bound.right, bound.front, bound.back
#bound.down is set automatically to reflecting in case gravity is
#switched on