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Reduce roundoff error on div(B) when using grid coarsening #284

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Merged
glesur merged 2 commits into from
Oct 23, 2024
Merged

Reduce roundoff error on div(B) when using grid coarsening #284

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3f5b740
reduce roundoff error when using coarsening
glesur Oct 19, 2024
f7fc679
update reference tag for new grid coarsening
glesur Oct 19, 2024
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2 changes: 1 addition & 1 deletion reference
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Submodule reference updated 4 files
+ − MHD/Coarsening/dump.ref.double.plm.idefix-rkl.ini.dmp
+ − MHD/Coarsening/dump.ref.double.plm.idefix-x2.ini.dmp
+ − MHD/Coarsening/dump.ref.double.plm.idefix-x3.ini.dmp
+ − MHD/Coarsening/dump.ref.double.plm.idefix.ini.dmp
42 changes: 33 additions & 9 deletions src/fluid/coarsenFlow.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -290,28 +290,52 @@ void Fluid<Phys>::CoarsenMagField(IdefixArray4D<real> &Vsin) {
// We reconstruct the parrallel field component with divB=0

int factor = 1 << (coarsening-1);


if( (index-begDir)%factor == 0) {
real qt = 0;
real qb = 0;

// Loop forward
for(int shift = 0 ; shift < factor-1 ; shift++) {
real qt = Vsin(BXt,k+kt+shift*koffset, j+jt+shift*joffset, i+it+shift*ioffset)
qt += Vsin(BXt,k+kt+shift*koffset, j+jt+shift*joffset, i+it+shift*ioffset)
* At(k+kt+shift*koffset, j+jt+shift*joffset, i+it+shift*ioffset)
- Vsin(BXt,k+shift*koffset, j+shift*joffset, i+shift*ioffset)
* At(k+shift*koffset, j+shift*joffset, i+shift*ioffset);
#if DIMENSIONS == 3
real qb = Vsin(BXb,k+kb+shift*koffset, j+jb+shift*joffset, i+ib+shift*ioffset)
qb += Vsin(BXb,k+kb+shift*koffset, j+jb+shift*joffset, i+ib+shift*ioffset)
* Ab(k+kb+shift*koffset, j+jb+shift*joffset, i+ib+shift*ioffset)
- Vsin(BXb,k+shift*koffset, j+shift*joffset, i+shift*ioffset)
* Ab(k+shift*koffset, j+shift*joffset, i+shift*ioffset);
#else
real qb = 0.0;
#endif

Vsin(BXn, k+(shift+1)*koffset, j+(shift+1)*joffset, i+(shift+1)*ioffset) =
((real) (factor-(shift+1))) / ((real)factor) *
1.0/An(k+(shift+1)*koffset, j+(shift+1)*joffset, i+(shift+1)*ioffset) *
(
Vsin(BXn, k+shift*koffset, j+shift*joffset, i+shift*ioffset) *
An(k+shift*koffset, j+shift*joffset, i+shift*ioffset)
- qt - qb
);
(Vsin(BXn, k, j, i) * An(k, j, i) - qt - qb);
}
// Loop backward
qt = 0;
qb = 0;

// Loop forward
for(int shift = factor-1 ; shift >=1 ; shift--) {
qt += Vsin(BXt,k+kt+shift*koffset, j+jt+shift*joffset, i+it+shift*ioffset)
* At(k+kt+shift*koffset, j+jt+shift*joffset, i+it+shift*ioffset)
- Vsin(BXt,k+shift*koffset, j+shift*joffset, i+shift*ioffset)
* At(k+shift*koffset, j+shift*joffset, i+shift*ioffset);
#if DIMENSIONS == 3
qb += Vsin(BXb,k+kb+shift*koffset, j+jb+shift*joffset, i+ib+shift*ioffset)
* Ab(k+kb+shift*koffset, j+jb+shift*joffset, i+ib+shift*ioffset)
- Vsin(BXb,k+shift*koffset, j+shift*joffset, i+shift*ioffset)
* Ab(k+shift*koffset, j+shift*joffset, i+shift*ioffset);
#endif

Vsin(BXn, k+shift*koffset, j+shift*joffset, i+shift*ioffset) +=
((real) shift) / ((real)factor) *
1.0/An(k+shift*koffset, j+shift*joffset, i+shift*ioffset) *
(Vsin(BXn, k+factor*koffset, j+factor*joffset, i+factor*ioffset)
* An( k+factor*koffset, j+factor*joffset, i+factor*ioffset) + qt + qb);
}
}
}
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