In this post, I am reporting of the relative difference between the analytic and COMSOL results.
The file by the name 'Main_thermo_refractive.m' found in the SVN was slightly modified to generate the difference plot.
The quantity plotted is the absolute value of the difference between the two results divided by the result given by COMSOL.
The plot is in a semilogx plot. It can be seen the maximum deviation goes to a maximum of 6%.
Also the difference is higher at the higher frequencies.
The plot shows two cases - the case for which 500 terms in the series were summed to get the analytic solution and second
is the case where 1000 terms were summed. The plot does not change much due to the number of terms being summed
showing that the convergence is fast.