SummationByParts sets ni = cctk_lsh[0] but then uses this (in Fortran code) to size the array in memory:

CCTK_REAL, dimension(ni,nj,nk), intent(IN) :: var

which will fail when cctk_lsh != cctk_ash that is when padding is used.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2632/summationbypart-assumes-cctk_lsh-cctk_ash