[GRASS-dev] New grass library and modules

[Michael Barton]

Soeren,

I echo Markus on this. It is an important step forward in the workhorse
engine underneath GRASS. I'm forwarding it to colleagues who will be
interested both in the analytical and parallel potential of this.

Thanks much.

Michael


On 1/24/07 9:12 AM, "Soeren Gebbert" <soerengebbert at gmx.de> wrote:

> Hi Markus,
> thanks for the compliment. :)
> 
> I hope this small library is the first step to
> establish parallel computation in grass, besides the MPI modules.
> 
> But important to say: this library only works in parallel on SMP or ccNUMA
> machines. This little presentation i made will explain a bit of the technical
> background (sorry its only available in German):
> 
> http://www-pool.math.tu-berlin.de/~soeren/grass/modules/grass-pde-lib/OpenMP_G
> PDE_presenation_handouts.pdf
> 
> Best regards
> Soeren
> 
> 
> Am Mittwoch, 24. Januar 2007 15:59 schrieb Markus Neteler:
>> Hi Soeren,
>> 
>> this looks really nice and will help to better establish GRASS
>> as GIS workhorse also for heavy computations.
>> 
>> You could submit this to Computer & Geosciences as article :)
>> 
>> Markus
>> 
>> On Mon, Jan 22, 2007 at 10:10:19PM +0100, Soeren Gebbert wrote:
>>> Dear developers,
>>> i would like to submit a new library and two modules based on the new
>>> library into cvs.
>>> 
>>> The new library called "gpde_lib" is designed to support the solution of
>>> partial differential equations within grass. The discretization of PDE's
>>> is based on raster and volume maps.
>>> I have implemented groundwater flow for two and three dimensions.
>>> Heat flow and solute transport are on my todo list.
>>> 
>>> All library functions start with a N_
>>> eg: N_create_les() or N_alloc_array_2d().
>>> 
>>> The current draft doxygen documentation is available here:
>>> 
>>> http://www-pool.math.tu-berlin.de/~soeren/grass/modules/grass-pde-lib/htm
>>> l/
>>> 
>>> I have implemented two modules based on the new library to solve confined
>>> and unconfined groundwater flow in two dimensions and confined
>>> groundwater flow in three dimensions. The two programs are still very
>>> basic and support only two boundary conditions (dirichlet and neumann).
>>> 
>>> The modules are called r.gwflow and r3.gwflow.
>>> 
>>> The grass PDE lib provied functions to create and solve lineare equation
>>> systems. Therefor different linear equation solvers are implemented:
>>> * LU decomposition for quadratic matrices (direct)
>>> * GAUSS elimination for quadratic matrices (direct)
>>> * CG method for quadratic and sparse matrices (iterative)
>>> * BiCGStab method for quadratic and sparse matrices (iterative)
>>> 
>>> The solvers and the creation of a linear equation system (matrix
>>> assembling) are parallelized with OpenMP http://www.openmp.org. The
>>> speedup of the solvers is quite good (IMHO):
>>> http://www-pool.math.tu-berlin.de/~soeren/grass/modules/screenshots/sgi_a
>>> ltix_cg_bench.png
>>> 
>>> The new library do not use functions of the gmath library to create
>>> vectors or matrices, or to solve a linear equation systems. There reasons
>>> are: 1.) I was quite unsure if the gmath library calls are thread safe
>>> 2.) I do not wanted to use function calls to get access to vectors and
>>> matrices for performance reasons
>>> 3.) I wanted to parallelize the equation solvers with OpenMP and therefor
>>> all vector and matrix operations i use
>>> 4.) I'm not very familiar with the gmath library
>>> 5.) I do not know which gmath functions need LAPACK or BLAS
>>> 
>>> If those question can be clarified, it should be possible to use gmath
>>> functions in the gpde library.
>>> The only problems i see for now are, that there are two different
>>> function calls to perform a LU decomposition and the gpde lib do not use
>>> the matrix and vector structures of the gmath lib.
>>> 
>>> I have implemented a lot of unit and integration tests on code basis,
>>> which will also be commited into cvs. Those tests assure the correct
>>> functionality of the lib. If the tests are compiled, a new module called
>>> test.gpde.lib is created and can be executed within grass to test all
>>> functions of the library. IMHO we should create a test structure for each
>>> library to check the correct functionality on function base.
>>> 
>>> If there are no objections against the library, i would like to commit it
>>> to cvs.
>>> 
>>> Best regards
>>> Soeren
>>> 
>>> _______________________________________________
>>> grass-dev mailing list
>>> grass-dev at grass.itc.it
>>> http://grass.itc.it/mailman/listinfo/grass-dev
>> 
>> _______________________________________________
>> grass-dev mailing list
>> grass-dev at grass.itc.it
>> http://grass.itc.it/mailman/listinfo/grass-dev
> 
> 

__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton