[Users] differences in results between two versions of ET

[Erik Schnetter]

Yosef

As Ian mentioned, there are two changes that may affect this:

(1) The way in which the shape of the buffer region and the restricted
region are determined may be different now, even if a grid has the same
number of grid points. The old way was inconsistent under certain
circumstances. If this is the case, then certain grid points that used to
be defined via interpolation are now defined via time interpolation or vice
versa. You can see such differences if you output the grid structure, e.g.
via setting Carpet::verbose or CarpetLib::output_bboxes. (The resulting
output may be difficult to read.)

(2) Carpet's prolongation operators are implemented differently and may be
more efficient. If so, you should be seeing differences at the round-off
level. If you see differences only at every other point, then this is
likely the case – every second point is copied from the coarse grid, the
points in between are interpolated. Carpet also contains self-tests to
ensure that the operators have the desired order of accuracy.

-erik

On Friday, July 27, 2012, Ian Hinder wrote:

> **
>
> Hi Yosef,
>
> I believe the code was reorganised in carpet and this needed the algorithm
> to change in a way that meant numerical results would change. I can't check
> right now, but this should have been mentioned in the announcement of the
> new version of carpet as well as the ET release notes.
>
> --
> Ian Hinder
> ian.hinder at aei.mpg.de <javascript:_e({}, 'cvml',
> 'ian.hinder at aei.mpg.de');>
>
>
> ----- Original message -----
> > While trying to understand why the results from a BBH run
> > differed when using the 2011_05 and 2011_10 version of ET
> > I noticed that the two versions gave different results on every
> > other point of the buffer region (in a 2 level run) on the 2nd
> > time level.
> >
> > I reran the test using McLachlan and I found a similar
> > behavior, but for fewer points (here, only 3, rather
> > than 8) and only the innermost points.
> >
> >
> > diff -w -u ~/ET/Old/Cactus/test/mc/gxx.x.asc ~/ET/Develop/Cactus/test/mc
> > | grep "^[+-]2"
> > -2          0 0 0 0 26 8 8  0.1        1.8 0 0 5.86163790879802
> > +2          0            0 0 0    26 8 8  0.1        1.8 0 0
> 5.86163790879801
> > -2          0 1 0 0 26 8 8  0.1        1.8 0 0 5.86163790879802
> > +2          0            1 0 0    26 8 8  0.1        1.8 0 0
> 5.86163790879801
> > -2          0 1 0 0 59 8 8  0.1        5.1 0 0 2.06954055131151
> > +2          0            1 0 0    59 8 8  0.1        5.1 0 0
> 2.06940807802512
> > -2          0 1 0 0 61 8 8  0.1        5.3 0 0 2.01672019300839
> > +2          0            1 0 0    61 8 8  0.1        5.3 0 0
> 2.01674238678588
> > -2          0 1 0 0 63 8 8  0.1        5.5 0 0 1.96875965038995
> > +2          0            1 0 0    63 8 8  0.1        5.5 0 0
> 1.96875664800624
> >
> >
> >
> > One of the major differences between these two versions of ET is the
> > switch from the git to hg version of carpet.
> >
> > Here is the full parfile that I used.
> >
> >
> #==============================================================================
>
> >
> > ActiveThorns = "admanalysis admbase admcoupling admmacros coordgauge
> > spacemask StaticConformal  boundary time cartgrid3d ioutil iobasic
> > nanchecker CoordBase aeilocalinterp Slab SphericalSurface LocalReduce
> > MoL Carpet CarpetInterp CarpetIOASCII CarpetLib CarpetReduce CarpetSlab
> > CarpetRegrid2 SphericalSurface CarpetIOHDF5 CarpetIOScalar InitBase
> > SymBase LoopControl GSL ReflectionSymmetry"
> >
> >
> > ActiveThorns = "TimerReport"
> >
> > TimerReport::out_every      = 512
> > TimerReport::out_filename = "TimerReport"
> > Carpet::output_timers_every = 512
> >
> #------------------------------------------------------------------------------
>
> >
> > # Run parameters
> >
> #------------------------------------------------------------------------------
>
> >
> > # Grid
> >
> > mol::ode_method                                              = "RK4"
> > mol::mol_intermediate_steps                      = 4
> > mol::mol_num_scratch_levels                      = 1
> >
> >
> >
> > CoordBase::domainsize            = "minmax"
> > CoordBase::xmin                        = 0
> > CoordBase::ymin                        = 0
> > CoordBase::zmin                        = 0
> > CoordBase::xmax                        = 10
> > CoordBase::ymax                        = 10
> > CoordBase::zmax                        = 10
> > CoordBase::spacing                  = "numcells"
> > CoordBase::ncells_x                = 50
> > CoordBase::ncells_y                = 50
> > CoordBase::ncells_z                = 50
> > CartGrid3D::type                      = "coordbase"
> > CartGrid3D::domain                  = "full"
> > CartGrid3D::bitant_plane      = "xy"
> > CartGrid3D::avoid_originx    = no
> > CartGrid3D::avoid_originy    = no
> > CartGrid3D::avoid_originz    = no
> >
> > CoordBase::boundary_size_x_lower              = 4
> > CoordBase::boundary_size_y_lower              = 4
> > CoordBase::boundary_size_z_lower              = 4
> > CoordBase::boundary_shiftout_x_lower      = 1
> > CoordBase::boundary_shiftout_y_lower      = 1
> > CoordBase::boundary_shiftout_z_lower      = 1
> >
> > CoordBase::boundary_size_x_upper              = 4
> > CoordBase::boundary_size_y_upper              = 4
> > CoordBase::boundary_size_z_upper              = 4
> >
> > ReflectionSymmetry::reflection_x = yes
> > ReflectionSymmetry::reflection_y = yes
> > ReflectionSymmetry::reflection_z = yes
> > ReflectionSymmetry::avoid_origin_x = no
> > ReflectionSymmetry::avoid_origin_y = no
> > ReflectionSymmetry::avoid_origin_z = no
> >
> >
> >
> > driver::ghost_size                                              = 4
> >
> > #-----------------------------------------------------------
>


-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/
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