LTE tests

In this test we have set $\epsilon_l=1$ to test the accuracy of the formal solution by comparing to the results of the 1D code. The 1D solver uses 64 radial points, distributed logarithmically in optical depth. In Fig. 2 we show the line mean intensities ${\bar J}$ as function of distance from the center for both the 1D ($+$ symbols) and the 3D solver. The results plotted in Fig. 1 show an excellent agreement between the two solutions, showing that the line 3D RT formal solution is comparable in accuracy with the corresponding 1D formal solution. Note that the difference of the distribution of spatial points (linear in the 3D case, approximately logarithmic in the 1D case) causes a much lower resolution of the 3D calculations in the central regions and in a higher resolution of the 3D calculations in the outer regions compared to the 1D test case.