int make_ic(int x, int y, int z) { int i, j, k; double velo_x, velo_y, velo_z; double T0, T, A, rho0, pre0;Here the constants for the implemented temperature distribution in a stratified atmosphere are defined.

//T(z)=T_0 + A*(z-z0) T0 = 288.15; //[K] A = -6.5E-3; //[K/m]Pressure and temperature at a certain level for the stratified atmosphere are assigned here.

rho0 = 1.229; // Density at sea level [kg/m^3] pre0 = 1.013E5; //pressure at sea level [N/m^2]In order to get a physical gas distribution we assign very

velo_x = small; velo_y = small; velo_z = small;If one needs a toy atmosphere to play around one has to switch in the

if (strat_const_atmos == 1) { for (i = 0; i < x; i++) { for (j = 0; j < y; j++) { for (k = 0; k < z; k++) { T = T0 + A * ((ymax / y) * j); rho[i][j][k] = rho0 * pow((T / T0), .... (-grav_acc / (gasconstant * A) + 1)); pre[i][j][k] = pre0 * pow((T / T0), .... (-grav_acc / (gasconstant * A))); vx[i][j][k] = velo_x; vy[i][j][k] = velo_y; vz[i][j][k] = velo_z; } } } }If one needs a homogeneous atmosphere one needs to switch in the

if (strat_const_atmos == 0) { for (i = 0; i < x; i++) { for (j = 0; j < y; j++) { for (k = 0; k < z; k++) { rho[i][j][k] = 1.2; pre[i][j][k] = 300 * gasconstant * rho[i][j][k]; vx[i][j][k] = velo_x; vy[i][j][k] = velo_y; vz[i][j][k] = velo_z; } } } } return 0; }Assuming your simulation should include an obstacle build by TYCHO you have to define the shape, density and temperature in the

/*! The form of the obstacle is defined in this function example of just a round thing. */ int initiate_domain(int x, int y, int z) { int i, j, k; for (i = 0; i < x; i++) { for (j = 0; j < y; j++) { for (k = 0; k < z; k++) { int i2 = i - x / 2.0; int j2 = j - y / 2.0; int xy = sqrt(i2 * i2 + j2 * j2); if (xy < x / 20) { dom[i][j][k] = 1; rho[i][j][k] = obstacle_density; pre[i][j][k] = obstacle_temperature; vx[i][j][k] = 0.0; vy[i][j][k] = 0.0; vz[i][j][k] = 0.0; } else { dom[i][j][k] = 0; } } } } printf("Initiate domain done\n"); return 0; }

To summarize, defining your own ICs in the **make_ic**-function requires full specification of the five 3-dimensional arrays **rho, pre, vx, vy, vz**. If 2 dimensional simulations are needed, then just assign 1 to the index **k**. Remember that this code strictly uses **SI**-units. Consequently a 1D simulation needs x=1, y=1 and z=1.