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				| <!-------- @HEADER
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|  !
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|  ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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|  !
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|  !  Zoltan Toolkit for Load-balancing, Partitioning, Ordering and Coloring
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|  !                  Copyright 2012 Sandia Corporation
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|  ! SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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|  !
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|  ! Questions? Contact Karen Devine	kddevin@sandia.gov
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|  !                    Erik Boman	egboman@sandia.gov
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| <a href="https://www.sandia.gov/general/privacy-security/index.html">Sandia Privacy and Security Notice</a></font></b></td>
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| 
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| <td VALIGN=TOP><!--MAIN CONTENT AREA STARTS HERE--><!----------------THIS IS A CHANGE AREA----------------><!------HEADER TEXT SHOULD BE REPLACE THIS TEXT------><b><font face="Verdana, Arial, Helvetica"><font size=+2>Zoltan: </font></font></b>
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| <br><b><font face="Verdana, Arial, Helvetica"><font size=+2>Parallel Partitioning, Load Balancing and Data-Management Services 
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| <p>
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| Frequently Asked Questions
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| </font></font></b>
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| <p><!---------------END OF THIS CHANGE AREA---------------><!----------------THIS IS A CHANGE AREA----------------><!--MAIN CONTENT SHOULD BE PLACED IN THE AREA BELOW-->
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| <!------------------------------------------------------------------------->
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| <!------------------------------------------------------------------------->
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| <!------------------------------------------------------------------------->
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| 
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| <hr WIDTH="100%">
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| <p>
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| <ol>
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| <!------------------------------------------------------------------------->
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| <!------------------------------------------------------------------------->
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| <!------------  Type questions here; hyperlink to answers below. ---------->
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| <!------------  Keep them in the same order!                     ---------->
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| <!------------------------------------------------------------------------->
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| <!------------------------------------------------------------------------->
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| <li>  <a href="#ZOLTANH">How do I upgrade from the Zoltan v1 interface (in
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| lbi_const.h) to the current Zoltan interface (in zoltan.h)?
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| <li>  <a href="#EMPTYPART">Zoltan's hypergraph partitioner
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| is returning empty parts, that is, parts that have zero
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| objects in them. Is this a bug?</a>
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| <li>  <a href="#MPILEAK">On some platforms, why do Zoltan partitioning 
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| methods RCB and RIB use an increasing amount of memory over multiple 
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| invocations?</a>
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| <li> <a href=#INTELF90">Why does compilation of the Fortran interface hang
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| with Intel's F90 compiler?</a>
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| <li>  <a href="#MPIRECVLIMIT">During runs (particularly on RedStorm), MPI 
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| reports that it is out of resources or too many messages have been posted.
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| What does this mean and what can I do?</a>
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| <li><a href="#MPIRECVLIMIT2">On very large problems, 
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| Zoltan communication routines fail in MPI_Alltoallv.
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| Why does this happen and what can I do?</a>
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| <li> <a href="#REALLOCBUG">Realloc fails when there is plenty of memory.  Is this a Zoltan bug?</a>
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| <li>  <a href="#DEPFILES">What does the following message mean during 
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| compilation of <i>zoltan</i>:  
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| Makefile:28: mem.d: No such file or directory
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| </ol>
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| <p>
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| <hr WIDTH="100%">
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| <hr WIDTH="100%">
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| <p>
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| <ol>
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| <!------------------------------------------------------------------------->
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| <!------------------------------------------------------------------------->
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| <!------------  Type answers here.                         ---------------->
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| <!------------  Keep them in the same order as list above! ---------------->
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| <!------------------------------------------------------------------------->
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| <!------------------------------------------------------------------------->
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| <hr WIDTH="100%">
 | |
| <li>  <a NAME="ZOLTANH"></a>How do I upgrade from the Zoltan v1 interface (in
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| lbi_const.h) to the current Zoltan interface (in zoltan.h)?
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| <p>
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| The Zoltan interface was revised in version 1.3 to include "Zoltan" in 
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| function names and defined types.  Upgrading to this interface is easy.
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| <ul>
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| <li>  Include "zoltan.h" instead of "lbi_const.h" in your source files.
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| <li>  For most Zoltan functions and constants, prefix "LB_" is replaced 
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| by "Zoltan_"; for example, "LB_Set_Param" is now "Zoltan_Set_Param."  
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| A few exceptions exist; for example, 
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| "LB_Balance" is Zoltan_LB_Balance; "LB_Free_Data" is "Zoltan_LB_Free_Data."
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| See the <a href="ug_html/ug_backward.html#Backward v1.3">Release v1.3
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| backward compatibility notes</a> for a complete list of name changes.
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| <li>  Fortran90 applications should define user-defined data 
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| in <i>zoltan_user_data.f90</i> rather than <i>lb_user_const.f90</i>.
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| </ul>
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| More complete details are in the 
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| <a href="ug_html/ug_backward.html#Backward v1.3">Release v1.3
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| backward compatibility notes</a>.
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| <hr WIDTH="100%">
 | |
| <li>  <a NAME="EMPTYPART"></a>Zoltan's hypergraph partitioner
 | |
| is returning empty parts, that is, parts that have zero
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| objects in them. Is this a bug?
 | |
| <p>
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| The hypergraph partitioner creates partitions with up to a specified amount
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| of load imbalance; the default value is 10% imbalance allowed, but the user
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| can tighten the load imbalance.  Any partition that satisfies the load
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| imbalance tolerance is a valid partition.  As a secondary goal, the
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| hypergraph partitioner attempts to minimize interprocessor communication.
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| Having a part with zero weight almost certainly reduces total communication;
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| the zero-weight part would not need to communicate with any other part.
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| <p>
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| So in some cases, Zoltan is generating a valid partition -- one that
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| satisfies the imbalance tolerance -- that happens to have lower total
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| communication if one of the parts is empty.  This is a good thing, but one
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| that some applications don't like because they didn't consider having zero
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| weight on a processor.
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| <p>
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| To try to avoid this problem, lower the imbalance tolerance so that
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| the partitioner is more likely to give work to all parts.  Change the value
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| of Zoltan parameter
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| <a href="ug_html/ug_alg.html#IMBALANCE_TOL">IMBALANCE_TOL</a>
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| to a smaller value; e.g., 1.03 to allow only 3% imbalance: <br>
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| <a href="ug_html/ug_interface_init.html#Zoltan_Set_Param">Zoltan_Set_Param</a>(zz, "IMBALANCE_TOL", "1.03");
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| <p>
 | |
| As an alternative, you may try one of Zoltan geometric methods, such as 
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| <a href="ug_html/ug_alg_rcb.html">RCB</a>,
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| <a href="ug_html/ug_alg_rib.html">RIB</a> or
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|  <a href="ug_html/ug_alg_hsfc.html">HSFC</a>, which do not have this property.
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| <p>
 | |
| We may in the future add a parameter to disallow zero-weight parts, but at
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| present, we do not have that option.
 | |
| 
 | |
| <hr WIDTH="100%">
 | |
| <li>  <a NAME="MPILEAK"></a>On some platforms, why do Zoltan partitioning 
 | |
| methods RCB and RIB use an increasing amount of memory over multiple 
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| invocations?
 | |
| <p>
 | |
| Zoltan partitioning methods RCB and RIB use MPI_Comm_dup and MPI_Comm_split 
 | |
| to recursively create communicators with subsets of processors.  
 | |
| Some implementations of 
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| MPI (e.g., the default MPI on Sandia's Thunderbird cluster) do not correctly
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| release memory associated with these communicators during MPI_Comm_free,
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| resulting in growing memory use over multiple invocations of RCB or RIB.  
 | |
| An undocumented workaround in 
 | |
| Zoltan is to set the TFLOPS_SPECIAL parameter to 1 (e.g., 
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| <a href="ug_html/ug_interface_init.html#Zoltan_Set_Param"><b>Zoltan_Set_Param</b></a>(zz,"TFLOPS_SPECIAL","1");), which causes an 
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| implementation that doesn't use MPI_Comm_split to be invoked.
 | |
| 
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| <hr WIDTH="100%">
 | |
| <li> <a NAME=INTELF90"></a>Why does compilation of the Fortran interface hang
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| with Intel's F90 compiler?
 | |
| <p>
 | |
| There is a bug in some versions of Intel's F90 compiler.  We know
 | |
| Zoltan's Fortran interface compiles with Intel's F90 compiler versions
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| 10.1.015 through 11.1.056.  We know that it does not compile with
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| versions 11.1.059, 11.1.069 and 11.1.072.  We reported the problem to 
 | |
| Intel, and we are told that the compiler bug is fixed in version 11.1 update 7,
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| which is scheduled for release in August 2010.  See this 
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| <a href="https://software.intel.com/en-us/forums/showthread.php?t=75385">Intel 
 | |
| Forum link</a> for more details.
 | |
| 
 | |
| <hr WIDTH="100%">
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| <li><a NAME="MPIRECVLIMIT"></a>During runs (particularly on RedStorm), MPI 
 | |
| reports that it is out of resources or too many messages have been posted.
 | |
| What does this mean and what can I do?
 | |
| <p>          
 | |
| Some implementations of MPI (including RedStorm's implementation) limit
 | |
| the number of message receives that can be posted simultaneously.  Some
 | |
| communications in Zoltan (including hashing of IDs to processors in the
 | |
| Zoltan Distributed Data Directory) can require messages from large numbers
 | |
| of processors, triggering this error on certain platforms. 
 | |
| <p>
 | |
| To avoid this problem, Zoltan contains logic to use AllToAll communication 
 | |
| instead of point-to-point communication when a large number
 | |
| of receives are needed.  The maximum number of simultaneous receives allowed
 | |
| can be set as a compile-time option to Zoltan.
 | |
| In the <a href="ug_html/ug_usage.html#TrilinosAutotools">Autotool build
 | |
| environment</a>, option <i>--enable-mpi-recv-limit=#</i> sets the 
 | |
| maximum number of simultaneous receives allowed.  The default value is 4.
 | |
| 
 | |
| <hr WIDTH="100%">
 | |
| <li><a NAME="MPIRECVLIMIT2"></a>On very large problems, 
 | |
| Zoltan communication routines fail in MPI_Alltoallv.
 | |
| Why does this happen and what can I do?
 | |
| <p>
 | |
| For very large problems, the values in the displacement arrays needed
 | |
| by MPI_Alltoallv can exceed INT_MAX (the largest integer that can be stored
 | |
| in 32 bits).  The solution to this problem is to make Zoltan avoid using
 | |
| MPI_Alltoallv and, instead, use point-to-point sends and receives.  The 
 | |
| compile-time option 
 | |
| in the <a href="ug_html/ug_usage.html#TrilinosAutotools">Autotool build
 | |
| environment</a> is <i>--enable-mpi-recv-limit=0</i>.
 | |
| 
 | |
| 
 | |
| <hr WIDTH="100%">
 | |
| <li> <a NAME="REALLOCBUG"></a>Realloc fails when there is plenty of memory.  Is this a Zoltan bug?
 | |
| <p>
 | |
| This problem has been noted on different Linux clusters running parallel
 | |
| applications using different MPI libraries and C++ libraries.  
 | |
| Realloc fails where a malloc call will succeed.  The source of the error has
 | |
| not been identified, but it is not a Zoltan bug.  The
 | |
| solution is to compile Zoltan with the flag <b>-DREALLOC_BUG</b>.  
 | |
| Zoltan will replace
 | |
| every realloc call with malloc followed by a memcpy and a free.
 | |
| 
 | |
| <hr WIDTH="100%">
 | |
| <li>  <a NAME="DEPFILES"></a>What does the following message mean during
 | |
| compilation of Zoltan?<br>
 | |
| Makefile:28: mem.d: No such file or directory</blockquote>
 | |
| <p>
 | |
| In the old "manual" build system for Zoltan, dependency files were
 | |
| generated for each source file <i>filename</i>.c.  The first time Zoltan 
 | |
| was built for a given platform, the dependency files do not exist.  
 | |
| After producing this
 | |
| warning, gmake created the dependency files it needed and continued
 | |
| compilation.
 | |
| <p>
 | |
| Newer versions of Zoltan use autotools or cmake for builds and, thus, do
 | |
| not produce this warning.  
 | |
| </ol>
 | |
| 
 | |
| <p>
 | |
| <hr WIDTH="100%">
 | |
| Updated:  August 2, 2010
 | |
| 
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