;This is very simple program that will make a total
;linear polarization map out of Q and U maps.  All
;you need to do is change the file names.
;To call the program in IDL, type .com fracpol.pro,
;then type fracpol and the program will make the file
;P.fits in the directory that you opened IDL in.  Be
;sure that you have this text file saved in the
;directory you are working in as fracpol.pro

pro fracpol

xx=mrdfits('if1ch2xx.fits')  ;put the xx map file name
yy=mrdfits('if1ch2yy.fits')  ;put the yy map file name
xy=mrdfits('if1ch2xy.fits')  ;put the xy map file name
yx=mrdfits('if1ch2yx.fits')  ;put the yx map file name
i=(xx + yy)/2
q=(xx - yy)/2
u=(xy + yx)/2
p=sqrt(q^2 + u^2)
writefits, 'I.fits', i    ;put the I map file name
writefits, 'Q.fits', q
writefits, 'U.fits', u
writefits, 'P.fits', p
end