Metis partition for tetrahedron element?

[dba2006]

while I using Metis partition for tetrahedron element by function METIS_PartMeshNodal, it seems the results are very chaotic, and elements of the same "color" are not contiguous. like this:

then I use METIS_MeshToDual to translate mesh to a dual graph and using METIS_PartGraphKway to partition，by setting options[METIS_OPTION_CONTIG] = 1, the result a still chaotic, and elements of the same "color" are not contiguous。

while For regular 8 node hexdron element，this issue does not occur.

Could any one help me how to partition the tetrahedron elements into a "contiguous" partition for parallel finite element calculate.

[dba2006]

for 8 node hexgron element, the partition are like this:

[gfaster]

You might want to make sure the MeshToDual routine is giving you the right number of components.

If you pass METIS_DBG_INFO (I believe, it might be a different debug flag), it will print out the number of connected components.

[dba2006]

thank you! I used metis in windows, I wandering "pass METIS_DBG_INFO" means I should built metis again or just apply METIS_DBG_INFO in my code? and I would like to ask whether Metis can directly provide a continuous partitioning for my finite element mesh, rather than just printing out the number of connected components.

[gfaster]

If you're using the C api, you'll want to set options[METIS_OPTION_DBGLVL] = <flags OR'd together>.

If you're using the gpmetis CLI program, you'll have to give the flags individually with --dbglvl=<integer value of flags OR'd together>

METIS/include/metis.h

Lines 337 to 348 in a6e6a2c

	typedef enum {
	METIS_DBG_INFO = 1, /*!< Shows various diagnostic messages */
	METIS_DBG_TIME = 2, /*!< Perform timing analysis */
	METIS_DBG_COARSEN = 4, /*!< Show the coarsening progress */
	METIS_DBG_REFINE = 8, /*!< Show the refinement progress */
	METIS_DBG_IPART = 16, /*!< Show info on initial partitioning */
	METIS_DBG_MOVEINFO = 32, /*!< Show info on vertex moves during refinement */
	METIS_DBG_SEPINFO = 64, /*!< Show info on vertex moves during sep refinement */
	METIS_DBG_CONNINFO = 128, /*!< Show info on minimization of subdomain connectivity */
	METIS_DBG_CONTIGINFO = 256, /*!< Show info on elimination of connected components */
	METIS_DBG_MEMORY = 2048 /*!< Show info related to wspace allocation */
	} mdbglvl_et;

The copy of Metis I have on my machine right now is super broken, so I can't easily check, but I believe that should give you some insight

Also, I just remembered that both minconn and contig settings are broken in upstream Metis, and judging by your mesh it's probable that you're running into that. I've fixed it in my fork, but that can't run on Windows for the time being. If you're able to share the graph in Metis's format, I can see if you're actually running into that. I haven't actually seen that bug cause significant data corruption, but given that this is a small regular mesh I wouldn't be surprised.

If that's not what you're running into, I would guess that the ncommon parameter in METIS_MeshToDual is too high. It should be 3 for a tetrahedral mesh.

I would make sure the ncommon parameter is correct before going into the contig and minconn rabbit holes since it's easy to check and the most likely culprit.

[dba2006]

adjncy.txt
eind.txt
eptr.txt
xadj.txt

thanks,this is my finite element mesh and the data after calling METIS_MeshToDual
and the ncomm is 3

int ncomm = 3;
int numflag = 0; //0base

                idx_t* xadj=NULL;
                idx_t* adjncy=NULL;
                int ierr = METIS_MeshToDual(&nelem, &nnode,eptr,eind,&ncomm,&numflag,&xadj,&adjncy);
                if (ierr != METIS_OK) { printf("MeshToDual failed!\n");  }

idx_t nparts = ranksize;

                idx_t objval;
                idx_t options[METIS_NOPTIONS];
                
                METIS_SetDefaultOptions(options);
                options[METIS_OPTION_PTYPE] = METIS_PTYPE_KWAY;
                options[METIS_OPTION_OBJTYPE] = METIS_OBJTYPE_VOL; //CUT:最小edge-cut  VOL 最小通信量
                options[METIS_OPTION_CONTIG] = 1;   /* 强制连通 */
                options[METIS_OPTION_DBGLVL] = 2;

idx_t ncon = 1;
ierr= METIS_PartGraphKway(&nelem, &ncon, xadj, adjncy,
NULL, NULL, NULL, &nparts,
NULL, NULL, options, &objval, epart);
if (ierr != METIS_OK) std::cout << "unsuccess!" << std::endl;
std::cout << "Metis Part success!" << std::endl;