= hc module = 
[[PageOutline]]
hc is a C-language implementation of a Hager & O'Connell (1981), semi-analytical, propagator matrix approach to solving for velocities and tractions
in spherical shell Stokes flow in the presence of only radially varying viscosity. 

This code is based on work by [http://www.geodynamics.no/STEINBERGER/ Bernhard Steinberger] who modified the original source from [http://eapsweb.mit.edu/people/person.asp?position=Faculty&who=hager Brad Hager] and [http://geophysics.harvard.edu/people/oconnell/oconnell.html Rick O'Connell]. 

Bernhard's F77 was rewritten in C by [http://geodynamics.usc.edu/~becker/ Thorsten Becker] and [http://www.es.mq.edu.au/GEMOC/Participants/AcademManag/CraigOneill/papers.html Craig O'Neill] in 2006 during the CIG mantle flow benchmarking effort. 

References
  - Hager, B. H. and O’Connell, R. J.  (1981). A simple global model of plate dynamics and mantle convection  J. Geophys. Res. 86, 4843
  - [http://www.geodynamics.no/STEINBERGER/papers/pepi00.pdf Steinberger, B. (2000). Slabs in the lower mantle - results of dynamic modelling compared with tomographic images and the geoid, Phys. Earth Planet. Inter., 118, 241.]
  - [http://www.geodynamics.no/STEINBERGER/papers/j.1365-246X.2006.03131.pdf Steinberger, B. and A. Calderwood (2006). Models of large-scale viscous flow in the Earth's mantle with constraints from mineral physics and surface observations, Geophys. J. Int., 167, 1461.]
  - [http://geodynamics.usc.edu/~becker/flow_code_project.051706.pdf Becker et al. (2006)]  Global flow code benchmark plan.

[wiki:screenshots Screenshot] of [wiki:hc_docu hc] run from within [wiki:download SEATREE]

[[Image(source:/trunk/doc/seatree/Screenshot-1.png, 50%)]]   


== Availability == 
A current version of hc can be found is included in the 
[wiki:download SEATREE distribution].

The development version of hc is hosted at [http://www.geodynamics.org/wsvn/cig/mc/1D/hc/trunk/ CIG's SVN server]. 

== Requirements ==

A C compiler such as gcc for command line functionality, GMT for advanced functionality.

== Installation ==

hc needs to be compiled before it can be used within SEATREE or as a standalone. This can be done automatically using the [wiki:download SEATREE installation process],
or by hand. To install hc by hand, extract the tar file, follow the instructions in the README, and type "make".

== Documentation == 

1. Use of hc within the Seatree environment is described in the [wiki:UserDocs Seatree user documentation]. 

2. Use of hc from the python command line interface is described in the python driver help page
{{{
> ../../../py-drivers/py-hc/calc_vel_and_plot.py -h
Usage: calc_vel_and_plot.py [options]

Options:
  -h, --help            show this help message and exit
  --compute=COMPUTE     0: only plot 1: compute velocities or tractions with
                        HC (default = 1)
  --cdir=COMPUTEDIR, --compute-dir=COMPUTEDIR
                        directory to store computation results
  --dfac=DFAC, --density-factor=DFAC
                        density file scaling factor (default = 0.25)
  --dsf=DSF, --density-scaling-file=DSF
                        density scaling factor file (depth-dependent, like
                        viscosity), overrides --dfac (default = )
  --dt=DENSTYPE, --density-type=DENSTYPE
                        density SH type (dshs is short Becker & Boschi
                        tomography type, default = dshs)
  --dm=DENSMODEL, --density-model=DENSMODEL
                        density model, assumes % anomalies (default =
                        /home/walter/becker/progs/src/seatree/py-drivers/py-
                        hc/example_data/smean.31.m.ab)
  --free-slip           use free slip boundary condition (default = True)
  --gmt-path=GMTPATH    path to GMT binarym if not in system path
  --hc=HCPATH, --hc-path=HCPATH
                        path to HC binary, if not in system path
  --layers=LAYERS       comma separated layers for velocity or traction
                        plotting (default = 21,15,6,2)
  --no-slip             use no slip boundary condition (default free slip)
  --plot=PLOT           for plotting, supply 1 or more of the following
                        options: 'g' to plot geoid, 'v' to plot plate
                        velocities, 't' to plot radial tractions, 'n' for none
                        (default = gvt)
  --pdir=PLOTDIR, --plot-dir=PLOTDIR
                        directory to store plots
  --pvel=PLATEVELF, --plate-velocity-file=PLATEVELF
                        use plate velocity boundary condition, overrides -f
                        and sets -n
  --verbosity=VERBOSITY
                        verbosity level between 0 and 3 (default = 1)
  --vf=VISCFILE, --viscosity-file=VISCFILE
                        viscosity file (default =
                        /home/walter/becker/progs/src/seatree/py-drivers/py-
                        hc/example_data/visc.C2)
Cleaning Up...

}}}

3. Use of the individual hc binaries is described in a [source:/trunk/modules/mc/hc/README.TXT readme file].