Protection against division by zero cooling.

See merge request !35

The demotes cautions that parts of the SED are zero to notes.
The following wc on auto shows that we have a large number of
these.  They are benign - they occur if we use a blackbody
that does go to zero far out in the Wien tail.  They are a
minor note about the SED rather than something deserving of
raising a caution.

the number of cautions in tsuite/auto went from

Alien20:auto:wc ~gary/cloudy/cautions.txt
  5267  72721 544951 /home/gary/cloudy/cautions.txt

to

Alien20:auto:wc cautions2.txt
  3846  64015 460146 cautions2.txt

These protect against division by zero.  Problems were exposed
by the lab sim posted in gtests / bugs / Mancini.  The
sim does get now much farther along but aborts when the line
stack becomes misaligned.

The sim is a lab plasma, so it is far from our home base, but we
should be able to compute it.  It is non-equilibrium.  It is
unclear why the cooling is zero - perhaps the total is net heating.

The changes seem safe since they are have never been needed and
will have no effect in most cases.

add three AGN SEDs

See merge request !34

Maryam Dehghanian added these three AGN SEDs that are being
actively used by the community in AGN research.  The updated
ReadMe.txt gives more information.

Resolve "Optimize column density fails for molecules"

Closes #452

See merge request !32

Uses quoted syntax, e.g. "CO", for species other than atomic ions.
This should recover the functionality without re-introducing the
anomalous behaviours of the c17_branch implementation.

Modify output routine to scale automatically with label widths.

See issue #437 for details

email of 2021 May 5
In the last few days, I've been collecting rates for
O i +e inelastic collisions. I started with Barklem,
A&A 462, 781-788 (2007) and tried to cast the rates into
Omega_ij strengths. After accounting for the partitioning
into the 3 fine-structure levels (lumped together by
Barklem), I was in a position to compare my Omega_ij with
those reported in the stout datafile. I was able to match
the Omega_ij for all transitions from the 1,2,3 levels
into the 4,5,6 levels, and also the 4-->5 transition.

I'm not able, however, to reproduce the Omega_ij values reported
in stout for the 1,2,3-->7 transition (from O(3P_J=2,1,0)
into the level at 9.52 eV). I didn't check the transitions
into more energetic states. The comments at the bottom of the
stout o_1.coll file (attached here for your reference) note
that there may be some inconsistencies. I'm also attaching the
values that I estimated myself for transitions within levels up
to 10 eV. I would appreciate your comments on this difference.
If you think it may be useful, I can send you a more extended
table with the Omega_ij for additional transitions.

Thank you!

   Antonio García Muñoz

Dr. Habil.
Planetary/Atmospheric Scientist
IRFU/DAP/LDE3
CEA Paris-Saclay
Bât. 703 Orme des Merisiers
91191 Gif-sur-Yvette Cedex, France
http://antoniogarciamunoz.wordpress.com/

Previous implementation had been intended to ignore values close to
underflow, but the number chosen was large enough to be a significant
source for low abundance species.  Tightening the criterion to cut the
step length if any negative abundance appears works fine after wide
testing, so seems like a better approach.

Bare numbers are used for multiplets in CSresolver and get_iso_statw.
Use of enums (ipDOUBLET, etc), instead, lends to more readable code.

We need to make sure that the fix in connection to the bug with the
order of the 'save species band' and 'init "honly.ini"' commands is
always exercised.

The form of th85rate has a different formula than hmrate. For photoreactions one should use th85rate, not the hmrate. Since, both the th85rate and hmrate  take coefficient values in a similar syntax style (for alpha, beta and gamma), an unintentional mistake happened by me for those reactions.

source/parse_atom_iso.cpp
The SPECIES command still used in some error messages
when the SPECIES command changed to DATABASE

docs/latex/hazy1/optimize.tex
Same mistake in doc for commands with VARY option

The function that computes the statistical weight for levels in He-like
species reports 4n^2 for all levels.  The 4 sums over both singlets and
triplets.  However, the ground has only a singlet state, no triplet.

This is the corollary of an earlier bug, which made the same mistake in
how the n-n' CS is broken up among the fine structure levels of a He-like
ground state.

The implementation omits the exponential term that appears in Eq. (8.30)
of Lebedev & Beigman, as it is folded in its conversion to a collision
strength.  Comment clarifies this point.

Fix bug in H2 line cooling

See merge request !25