shade.rel.sh

[John Stallings]

To anyone who knows:
I am currently using GRASS4.1 for my masters thesis project at the 
University of Arizona.  I need information on how the shell script 
program called- shade.rel.sh -was created.  The formula is listed in the 
g.manual pages, but an explanation was not given as to the methodology 
behind it.  I am looking at how topography effects incoming solar 
radiation.  I need to know if the program looks at surrounding pixels and 
specifically how it creates the category file (0-dark, 100-light).  
Please, if there is anyone out there that can help me with this question 
I would greatly appreciate it.  Thank you.  
Just in case my e-mail address doesn't get passed along it is as follows:
jps at neurobio.arizona.edu