Grains

GrainsZero - called by zero before commands parsed, 
GrainsInit - called by opacity create after commands are parsed

the grains only exist after routine OpacityCreateAll is called 

mie.c contains the Mie scattering code originally written by Peter Martin,
and brought into Cloudy by Peter van Hoof, who is responsible for most of the 
current implementation.  

The .szd files are size distribution files. The 0m???.szd files define single
sized grains, and ism.szd, orion.szd define the obvious size distributions. If
you compile mie.c with

cc -ansi -Ofast -DSTANDALONE mie.c -lm

the executable will produce a file silicate_ism_20.opc. You can compare that
with the version included in the distribution. If you compile mie.c without the -DSTANDALONE, it
should link into Cloudy. If you run the following simple test run

title jones test
table ism
extinguish column=22 leak=0
hden 0
constant density
pgrains 0. type 18 binary "silicate_ism_20.opc"
stop zone 1

It should produce the attached output jones.out.

=====================================================

The total projected area (cm^2) in all grain species is
area = 0;
for(nd=0; nd<gv.nBin; ++nd)
{
	/* IntArea is area per grain size bin, cm+2
	 * conv_H_pCM3 units cm-3 */
	area += gv.bin[nd]->IntArea/4. * gv.bin[nd]->cnv_H_pCM3;
}

density of element ipX in grain species nd: