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TPC: fix the weight and grid scaling of the spline derivatives in addCorrections #15994

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alcaliva merged 2 commits into from
Oct 21, 2026
+10 −7
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TPC: fix the weight and grid scaling of the spline derivatives in addCorrections #15994

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f390389
TPC: fix the weight scaling of the mixed spline derivative in addCorr…
matthias-kleiner Oct 21, 2026
cdbce61
TPC: fix the chain-rule grid factors in addCorrections
matthias-kleiner Oct 21, 2026
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17 changes: 10 additions & 7 deletions Detectors/TPC/calibration/src/TPCFastSpaceChargeCorrectionHelper.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -1059,7 +1059,8 @@ void TPCFastSpaceChargeCorrectionHelper::addCorrections(
constexpr int nKnotPar3d = nKnotPar1d * 3;

{ // scale the main correction
double parscale[4] = {secMainScale, secMainScale, secMainScale, secMainScale * secMainScale};
// a spline is linear in its parameters: scaling the function scales all of them, the mixed derivative included
double parscale[4] = {secMainScale, secMainScale, secMainScale, secMainScale};
for (int iknot = 0, ind = 0; iknot < spline.getNumberOfKnots(); iknot++) {
for (int ipar = 0; ipar < nKnotPar1d; ++ipar) {
for (int idim = 0; idim < 3; idim++, ind++) {
Expand Down Expand Up @@ -1097,10 +1098,11 @@ void TPCFastSpaceChargeCorrectionHelper::addCorrections(

auto& linfo = corr.getRowInfo(row);

double scaleU = rowInfo.gridMeasured.getYscale() / linfo.gridMeasured.getYscale();
double scaleV = rowInfo.gridMeasured.getZscale() / linfo.gridMeasured.getZscale();
double scaleRealU = rowInfo.gridReal.getYscale() / linfo.gridReal.getYscale();
double scaleRealV = rowInfo.gridReal.getZscale() / linfo.gridReal.getZscale();
// chain rule for the derivatives: u = (y - y0) * yScale, v = (z - z0) * zScale => d/du_main = (du_corr / du_main) d/du_corr
double scaleU = linfo.gridMeasured.getYscale() / rowInfo.gridMeasured.getYscale();
double scaleV = linfo.gridMeasured.getZscale() / rowInfo.gridMeasured.getZscale();
double scaleRealU = linfo.gridReal.getYscale() / rowInfo.gridReal.getYscale();
double scaleRealV = linfo.gridReal.getZscale() / rowInfo.gridReal.getZscale();

for (int iu = 0; iu < gridU.getNumberOfKnots(); iu++) {
double u = gridU.getKnot(iu).u;
Expand All @@ -1116,7 +1118,8 @@ void TPCFastSpaceChargeCorrectionHelper::addCorrections(
float lu, lv, ls;
corr.convLocalToGrid(sector, row, y, z, lu, lv, ls);
ls *= scale;
double parscale[4] = {ls, ls * scaleU, ls * scaleV, ls * ls * scaleU * scaleV};
// knot parameters: {S, dS/dv, dS/du, d2S/dudv}
double parscale[4] = {ls, ls * scaleV, ls * scaleU, ls * scaleU * scaleV};
const auto& spl = corr.getSplineForRow(row);
spl.interpolateParametersAtU(corr.getCorrectionData(sector, row), lu, lv, P);
for (int ipar = 0, ind = 0; ipar < nKnotPar1d; ++ipar) {
Expand All @@ -1132,7 +1135,7 @@ void TPCFastSpaceChargeCorrectionHelper::addCorrections(
float lu, lv, ls;
corr.convRealLocalToGrid(sector, row, y, z, lu, lv, ls);
ls *= scale;
double parscale[4] = {ls, ls * scaleRealU, ls * scaleRealV, ls * ls * scaleRealU * scaleRealV};
double parscale[4] = {ls, ls * scaleRealV, ls * scaleRealU, ls * scaleRealU * scaleRealV};

{ // inverse X correction
corr.getSplineInvXforRow(row).interpolateParametersAtU(corr.getCorrectionDataInvX(sector, row), lu, lv, P);
Expand Down
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