Here is a list of all files with brief descriptions:

addprm.f90
anxlk.f90
assgnc.f90
basis.f90
basisc.f90
bessel.f90
bincom.f90
BL05CHSA.py
brent.f90
c16pc371e.py
caldlm.f90
catch.c
ccrints.f90
cd2km.f90
cfs.f90
cgltri.f90
confc.f90
convtc.f90
correl.f90
covar.f90
covrpt.f90
cscg.f90
datac.f90
daxpy.f90
dchex.f90
dcopy.f90
ddot.f90
dfunc.f90
drotg.f90
dtime.c
enorm.f90
eprls.f90
eprmat.f90
eprprm.f90
errmsg.f90
expdat.f90
fitc.f90
fitl.f90
fixc.f90
fmomnt.f90
fortrancall.h
ftfuns.f90
ftwork.f90
fz.f90
gconvl.f90
genio.c
getdat.f90
helpc.f90
ipar.f90
ipsfind.f90
iterat.f90
l1pfun.f90
lbasix.f90
lcheck.f90
letc.f90
lfun.f90	This seems to be the central hub, which is called by the L-M optimization, and which calls the functions that generate the simulated spectrum
lgrint.f90
lmcom.f90
lmnls.f90
lmpar.f90
lpnam.f90
lprmpt.c
matrll.f90
maxl.f90
mnbrak.f90
momdls.f90
mspctr.f90
mtsdef.f90
nlsdim.f90
nlsl.f90
nlsnam.f90
ordrpr.f90
parc.f90
parcom.f90
parsav.f90
physcn.f90
pidef.f90
plgndr.f90
pltx.c
pltx_dummy.c
pmatrl.f90
pstvec.f90
qrfac.f90
qrsolv.f90
qrutil.f90
rmvprm.f90
rnddbl.f90
scalec.f90
scmvm.f90
series.f90
setmts.f90
setnm.f90
setprm.f90
setspc.f90
shiftc.f90
sitec.f90
srchc.f90
sscale.f90
sshift.f90
statc.f90
stats.f90
stdio.f90
strutl1.f90	I/O UTILITY ROUTINES FOR NLS COMMAND INTERPRETER
strutl2.f90
stvect.f90
symdef.f90
tdchek.f90
tdsqz.f90
tensym.f90
testmods.f90
timer.f90
tridag.f90
varyc.f90
w3j.f90
writec.f90
writr.f90
zaxpy.f90
zaypx.f90
zdotu.f90