Computing the vertex separators

Dear Professor,

for the purpose of a substructuring domain decompositioning method I want to implement, I need to have access to the separators between the various subdomains. I was thinking of using the METIS_PartMeshNodal-function to partition the mesh in N subdomains and subsequently calling METIS_NodeComputeSeparator to calculate the separators between the subdomains. Is this the most appropriate approach to this problem? It is not entirely clear to me how METIS_NodeComputeSeparator works. Does it calculate a new partition? Or will it calculate the separator between the domains PartMeshNodal has defined?

thanks,
Vincent