# [petsc-users] metis version of petsc - segmentation fault

Alexandre Halbach alexandre.halbach at gmail.com
Thu Aug 25 11:37:25 CDT 2022

```Hello,

I am using the metis package provided by the latest petsc version, using
issue but since metis is used in petsc and mumps this seems relevant to ask
here too.

I systematically get a segmentation fault on this metis version (didn't try
others) when I partition even simple and not too large graphs ( O(5
millions)). I tried a lot of cases as well as both the 32 and 64 bits
version of petsc and also increasing ulimit (on Linux).
Here is the shortest possible representative example with that problem
(c++). I double checked it and I hope there is no mistake in this example.
The below example constructs the containers for a 1D line graph (n vertices
connected by edges one by one as in a chain. Both end vertices only have a
single neighbor while all other vertices have two neighbors).
Either this is something I am doing wrong or there is a bug in at least the
metis version proposed in petsc.

Here is the example producing a segfault. If you don't get a segfault try a
10 millions or more vertices graph.

Alex

#include "metis.h"

int main(void)
{
// Number of vertices:
int n = 1000000;
// Addresses should for example be [0 1 3 5 7 8] for 5 vertices
for (int i = 2; i < n; i++)

// Connected vertices should for example be [1 0 2 1 3 2 4 3] for 5
vertices
idx_t connectivities[2*(n-1)];
connectivities[0] = 1;
for (int i = 1; i < n-1; i++)
{
connectivities[2*i-1] = i-1;
connectivities[2*i+0] = i+1;
}
connectivities[2*(n-1)-1] = connectivities[2*(n-1)-2]-1;

idx_t nvtxs = n;
idx_t nEdges = n-1;

idx_t metisOptions[METIS_NOPTIONS];
METIS_SetDefaultOptions(metisOptions);
metisOptions[METIS_OPTION_NUMBERING] = 0; // c numbering (start at 0)

idx_t ncon = 1;
idx_t nParts = 2;
idx_t objval;
idx_t part[nvtxs];

int ret = METIS_PartGraphRecursive ( &nvtxs, &ncon, addresses,
connectivities, NULL, NULL, NULL, &nParts, NULL, NULL, metisOptions,
&objval, part );
}
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```