Documentation/UserGuide/Problem Block

Parameters in this block are accessed by the problem-generator, and therefore depend on the problem being run. For example, the problem-generator ./athena4.0/src/prob/shkset1d.c (which is used for the Brio & Wu test problem) requires the following parameter values in the <problem> block:

<problem>
gamma           = 2.0       # gamma = C_p/C_v
shk_dir         = 1         # Shock Direction -- (1,2,3) = (x1,x2,x3)

dl              = 1.0       # density on left half of grid
pl              = 1.0       # pressure
v1l             = 0.0       # X-velocity
v2l             = 0.0       # Y-velocity
v3l             = 0.0       # Z-velocity
b1l             = 0.75      # X-magnetic field
b2l             = 1.0       # Y-magnetic field
b3l             = 0.0       # Z-magnetic field
s0l             = 1.0       # "color"

dr              = 0.125     # density on right half of grid
pr              = 0.1       # pressure
v1r             = 0.0       # X-velocity
v2r             = 0.0       # Y-velocity
v3r             = 0.0       # Z-velocity
b1r             = 0.75      # X-magnetic field
b2r             = -1.0      # Y-magnetic field
b3r             = 0.0       # Z-magnetic field
s0r             = 0.0       # "color"

The only parameter values in the <problem> block that are common to all input files are:

gamma: ratio of specific heats, only used for adiabatic EOS.

iso_csound: isothermal sound speed, only used for isothermal EOS.

All of the remaining parameter names in the example above are specific to the Brio & Wu shocktube problem. In general, the input file for other problems will have different variable names in the problem block.