The difference of prinicipal stresses and their directions are found
out from the photoelastic patterns. The Question is to  use this data
obtained from the photoelastic method and separate the principal
stresses using any numerical technique. There  are methods like
multigrid algorithm and many more to serve this purpose.  The coding
for this numerical technique is to be  written in either matlab or
C/C++. I would appreciate if you could write a program for any
numerical method that would  separate the stresses.

You can use any numerical technique. This doesn't need to be done in
one day. it's ok if you take more than that, may be around one week
for the solution.

I shall provide you with links to some papers on multigrid method. 

http://80-ej.iop.org.floyd.lib.umn.edu/links/q72/tWNMI8QoPvblWWRSYWD9WQ/e80809.pdf

http://www.llnl.gov/casc/people/henson/mgtut/ps/mgtut.pdf



I would appreciate your help.  

Thank you!
Laxman