[CIG-SHORT] Pylith "zero-pivot" error

[Ravi Kanda]

Brad,

Thanks, the debugging suggestion was very helpful.  Pylith now "understands" my
CFG files. But now, the run fails with the "Detected zero pivot in LU 
factorization" error (see attached screen output log).  After checking the PETSc 
documentation page, I tried running with the following in my PYLITHAPP.CFG file:
---------------------------------------------
pc_factor_shift_nonzero = true
#pc_factor_shift_positive_definite = true
---------------------------------------------

A. I get the same error with either/BOTH flags.

B. I then ran pylith with the mesh debug flag, "debug = 1", and it seems like 
the problem is with element 2982 (?).  On further investigation of the screen 
output, this turns out to be a cohesive element.  So, I am trying to figure out 
whether there is a problem of mesh-quality or if it has something to do with 
cohesive element generation.

C. I used Cubit to generate my mesh, and have visually checked the mesh quality 
to make sure there are only a small number of elements with a poor aspect ratio 
(and no negative Jacobians).  The imported mesh has 1265 elements (and only 4 of 
those elements have "bad" aspect or edge ratios - i.e. > 4.0).  I am not sure 
if/how Pylith re-numbers the imported elements, especially after the cohesive 
elements are added to the system - so, I don't know where this element is in the 
mesh.  Is it possible to extract this from the pylith debug information?  I 
couldn't find any coordinate info listed in the screen output.

D. Also, there are two more error "blocks" starting at lines 134122 and 134167 
of the attached log file.  Are these associated with the zero pivot error above 
(line 134077)?

Thanks again!
Ravi.

----------------------------------------------------------------------------------

Brad Aagaard wrote:
> Ravi-
> 
> You have an error when specifying the materials bin. Delete line 38 of 
> SLAB2D_p2_nx101_Th30.cfg. 
> 
> What you have translates to:
> pylith.timedependent.materials.materials = slab2D_3M
> what you mean is:
> pylith.timedependent.materials = slab2D_3M
> 
> The easiest way to track down these problems is to use 
> the --help, --help-properties, and --help-components arguments to pylith. For 
> example, if you ran PyLith with
> pylith YOUR_CFG_FILES_HERE --timedependent.help-components
> you would find out that PyLith is still using the default materials bin 
> (homogeneous). Once you fix your error you should see that PyLith is picking 
> up your setting on line XX of your cfg file.
> 
> Brad
> 
> 

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Ravi Kanda
Seismological Laboratory, MC 252-21
Division of Geological and Planetary Sciences
California Institute of Technology

1200 E. California Blvd., Pasadena, CA 91125
Phone: 626-395-6971, Fax: 626-564-0715
Web Page: http://www.gps.caltech.edu/~rkanda

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For a human being, the unexamined life is not worth living - SOCRATES

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