[Trilinos-Users] Question about Zoltan and the Zoltan_RCB_Box function

Devine, Karen D kddevin at sandia.gov
Mon Dec 13 15:38:12 MST 2010


RCB partitions 1D, 2D, or 3D space, and assigns regions of space to
processors.  The region of space assigned to processors is not restricted by
the bounding box of the objects passed to Zoltan for partitioning.  Instead,
the regions of space extend to infinity.  This feature is useful for contact
simulations, where applications need to know the processors associated with
a point in space, not with a given object used in partitioning; the points
in space may be outside the initial bounding box of the objects passed to
Zoltan.   Zoltan_RCB_Box reflects this design, returning -DBL_MAX or
+DBL_MAX to indicate a part extends to infinity in some direction.

A bug in the input data for the simpleRCB.c example, however, caused the odd
results that you reported.  The coordinates in file mesh.txt in the example
directory are listed in (y,x) order rather than (x,y) order.  The routine
that prints the decomposition assumes the (x,y) order.  So the results from
Zoltan_RCB_Box look incorrect.

I attach a fixed mesh.txt file for you to use as input to simpleRCB.c.  We
are saving this change in the repository as well.

Thank you for your input and for clueing us in to a problem.


On 12/13/10 1:27 PM, "M. Scot Breitenfeld" <brtnfld at uiuc.edu> wrote:

> Hi,
> I don't understand how to get the correct values for xmin, ymin, xmax,
> ymax returned by Zoltan_RCB_Box
> When I add the function to the simpleRCB.c in example/C (Trilinos 10.6),
> adding:
> Zoltan_Set_Param(zz, "KEEP_CUTS", "1");
> Zoltan_Set_Param(zz, "NUM_LOCAL_PARTS","3");
> and placed Zoltan_RCB_Box after the call to Zoltan_LB_Partition
> Running the example on one processor (i.e. I want 3 parts) the output
> looks good:
> Mesh partition assignments after calling Zoltan
> 2-----2-----2-----2-----2
> |     |     |     |     |
> 2-----2-----2-----2-----2
> |     |     |     |     |
> 0-----0-----1-----1-----1
> |     |     |     |     |
> 0-----0-----1-----1-----1
> |     |     |     |     |
> 0-----0-----1-----1-----1
> but, for example part =1, the xmin,ymin,xmax,ymax is
> -DBL_MAX,2,3,-DBL_MAX/,/ why is it not giving the bounding box
> coordinates? Is there an additional parameter I need to added? Zoltan
> doesn't return any errors. I could not get it to return the correct
> values when I remove the NUM_LOCAL_PARTS and ran it on multiple
> processors either.
> Scot/
> /
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> Trilinos-Users at software.sandia.gov
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