Apol.f90 is a Fortran 90 program to extract the polarization
and limb darkening from any plane-parallel atmosphere 
where we know (1) the variation of B_nu(tau_nu) and (2)
the ratio of pure absorption to total extinction 
(i.e., lambda_nu = kappa_nu/(kappa_nu+sigma_nu)). 
The file fort.4 contains a list of 80 optical depth
points 0<= tau_nu <=22. The user must supply the values
of B_nu and lambda at these (monochromatic) optical
depths.

Compile with
              gfortran Apol.f90 -o Apol
and run with
             ./Apol < B-lam.data > output

Here, B-lam is a file with 80 rows and two columns
containing the B_nu and lambda_nu values for each 
tau_nu. You supply this data from your model atmosphere.
(The "B-lam.data" file included is just an example.)
You need to have the fort.1, fort.2, etc. files in
the same directory as the program needs to read them.

The output file gives (1st 80 rows):
(1) the values of s(tau) and p(tau) for the model
and then the emergent radiation in 159 rows:
(2) the values of I(mu) and Q(mu) for a dense grid
    of mu values (159 values, concentrated toward
    the limb - mu values near 0).