[petsc-users] MatSetNearNullSpace() or PCSetCoordinate for GAMG ?

[A.L. Siahaan]

Referring to the following thread about setting nullspace and coordinate 
for GAMG : 
http://lists.mcs.anl.gov/pipermail/petsc-users/2012-April/012790.html

Is there any difference of memory requirement (to set nullspace) between 
MatSetNearNullSpace() and PCSetCoordinate ?

For PCSetCoordinate, is the order of x-y-z coordinate in thevector [0.x, 
0.y, 0.z, 1.x, ..., N-1.z] with respect to the ordering of solution vector 
[0.u_x, 0.u_y, 0.u_z, 1.u_z, ..., N-1.u_z] ?

I tried to use PCSetCoordinate for GAMG, but then I get an error :
============================================================
[0]PETSC ERROR: Floating point exception!
[0]PETSC ERROR: Infinite or not-a-number generated in mdot, entry 0!
========================================================

I am wondering if it is due to the ordering of coordinate.

Regards,
Antony