$setcountedexitlength

$setcountedexitlength is a special function to set the smallest region size to count the photon density. This is simply to avoid some problems of output plot. When we set up the region to detect the final stop point of photon, it should be distributed smoothly if we ran many photons. However, if the region length is too small such as 1 nm, then the photon density might be too large even if only 1 photon is stop at this location. Then we will obtain abnormal large peak in certain range. To avoid these problem, the program will not calculate the photon density at this region.