title compare with Van Blerkom and Hummer exact RT results
c
c commands controlling continuum =========
blackbody 50000 K
phi(h) 12.30103
c commands for density & abundances =========
hden 4
init "honly.ini"
abundances all -10
c
c commands controlling geometry  =========
stop efrac -0.5
c
c other commands for details     =========
diffuse ots
no level2 lines
constant temper 4
iterate
c
c commands controlling output    =========
save performance "limit_vbhum.per"
save monitors last "limit_vbhum.asr"
save overview last "limit_vbhum.ovr"
save dr last "limit_vbhum.dr"
c
c commands giving the monitors    =========
monitor thickness 16.886
// >>chng 01 apr 01, from 55 to 65, change eden zoning
// >>chng 04 mar 04, from 65 to 75, improv conv
// >>chng 08 dec 08, from 75 to 69, upper limit -> equals (r2515)
// >>chng 08 dec 13, from 69 to 70, merging newsolvers branch
monitor nzone 70 error 0.01
//
monitor hydrogen ionization 1 -1.714
monitor line "Ca B" 4861 1.000
monitor line "Bac " 3646 15.24
//
// >>chng 05 mar 28, from 5 to 3.5, impr mol converg
// >>chng 08 dec 08, from 3.5 to 2.696, upper limit -> equals (r2515)
// >>chng 08 dec 13, from 2.696 to 3.429, merging newsolvers branch
// >>chng 09 jun 26, from 3.429 to 3.571, remove several dampers
// >>chng 12 oct 22, from 3.571 to 3.329, zone tau in rt_line_one
monitor itrzn 3.329 error 0.02
c 
c limit_vbhum.in
c 
c class limit 
c ========================================
c 

This is a test of the treatment of the diffuse fields, their transfer,
and their effects on the ionization structure of a nebula. The comparison
is made against the exact calculation published by Van Blerkom and
Hummer (1967). The geometry is open, that is, similar to that assumed
in most BLR calculations. 

>>refer	H	ionization	Van Blerkom, D., & Hummer, D. G. 1967, MNRAS, 137, 353

The diffuse ots command is entered in order to reproduce the
Van Blerkom and Hummer results.  The default assumption, outward only,
does not agree as well.  I changed the default from OTS to outward only
to be in better agreement with predictions by Harrington and Rubin
at the Lexington meeting.  They have not checked whether their codes
are in agreement with the Van Blerkom and Hummer paper.

Checks:
-	Neutral fraction at illuminated face 5.8*10-4.
-	Location of ionization front at 7.8*1016 cm.
-	34TOTL 486134 and 34CA B 486134 agree;  both slightly lower than 34Q(H) 486134.
-	Answers with OTS agree with 1967 results.

test hydrogen ground state rec effic against vb+h exact results
this is their case e) - "zero condition"
their answer for H0/Htot at the illuminated edge is approx 5.8E-4,
and a Stromgren radius of approximately 7.7E16 cm