The source code cvir.f implements the toy model outlined in Bullock et
al.  (2001).   This model reproduces  the  observed  mass and redshift
dependence  of dark  matter halo concentrations  as  derived from high
resolution N-body simulations.  It also returns the observed spread in
concentrations for a fixed mass and redshift.  Our observed spread
in log_10(cvir) is 0.14 (not 0.18 as is stated *incorrectly* in the
abstract.)  This has been corrected in Wechsler et al. (2002), which
should be referenced as our view of the intrinsic scatter.  The scatter
result has been confirmed by Maccio' et al. 2006.    Note that
this is larger than that reported by Jing (1999).  


The cvir.f code requires an input sigma(M) mass power
spectrum to run.  I've included an example for the lcdm model
you're running here called "sigma_lcdm".  The code sM.f generates
the sigma(M) file in case you want to change cosmology.

*If you want the original B01 model use: cvir.f  

*If you want our group's  latest (probably best) estimate for c(M) use cvir5.f.  This uses the K and F paramters quoted by Wechsler et al. 2006

*If you want the latest  estimate for c(M) from Maccio' et al. 2007 use cvir2.f  This uses the K and F paramters found by Maccio' et al. 2007 to match lower mass halos.
 
*If you aim to obtain characteristic halo formation times  as defined
using the Wechsler formula use : cvir3.f

*If you want results for large, cluster-size halos in Maccio et al., use: cvir4.f (note that this version is also close to our favored values quoted in Wechsler et al. 06 and listed in cvir5.f)

The file "sM_in.dat" allows you to specify the cosmological parameters
for the power spectrum you want to generate, and the top line
of the file allows you to give the model a name (I've chosen "lcdm"
here).  The name must be 4 characters long.  

The cvir.f code reads in the  same input file (sM_in.dat) and uses the
model name to know which power spectrum input file to use.
I have supplied a power spectrum for standard LCDM and the WMAP year three
best-fit.  This version has a lower sigma8 and will produce lower c's at fixed M.

When you compile cvir.f and run it  it will propt you for the mass and
then  the  redshift of  the  halo.  Enter  the  mass  in h^-1
solar  masses (e.g. 1.e11).

The programs  can be compiled with  g77.

If   you have  any  trouble   or  questions,  you  can contact   me at
jbullock@cfa.harvard.edu

Note that our definition of concentration cvir = Rvir/Rs, differs from
that of  NFW (cnfw = R200/Rs).  In  the end, the  derived profiles are
identical and this  is just a matter of  definition.  If you prefer to
use  cnfw, the  conversion is straightforward  (see  the NFW papers or
Bullock  et al. 2000 for details).   Unfortunately,  the conversion is
dependent  on   cosmology and   redshift.    For  SCDM,  cnfw  =  cvir
(approximately)    for  all redshifts.    For  LCDM,  cnfw = cvir/1.25
(approximately) at z=0, and cnfw = cvir (approximately) for z > 2.

See Wechsler et  al. (2002) for a   detailed investigation into  the 
origin of halo concentration scaling laws, scatter, etc.

In this routine cvir2.f, we have set F=0.015 and K=4.15.  Set to these
values, the  returned z_c  can be  used as input  for the  Wechsler et
al. 2002  formula for M(z),  mass accretion histories with  S=2.0.  In
terms of  W02 Equation 5  set S=2 and  a_c = 1./(1+z_c), where  z_c is
returned from this routine