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Normalize run weights before stochastic event distribution #164

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Merged
maureeungaro merged 1 commit into from
Jun 13, 2026
Merged

Normalize run weights before stochastic event distribution #164

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13 changes: 11 additions & 2 deletions gemc/eventDispenser/eventDispenser.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -104,10 +104,19 @@ void EventDispenser::distributeEvents(int nevents_to_process) {
mt19937 generator(randomDevice());
uniform_real_distribution<> randomDistribution(0, 1);

// Weights in the run-weights file are relative, not required to sum to 1. Compute the total
// once and scale each draw by it, so non-normalized weights distribute events correctly.
double totalWeight = 0;
for (const auto& weight : runWeights) { totalWeight += weight.second; }
if (totalWeight <= 0) {
log->error(ERR_EVENTDISTRIBUTIONFILENOTFOUND,
"Run weights sum to ", totalWeight, " (must be > 0). Check your run weights file.");
return;
}

// For each event, select a run by comparing a random draw to the cumulative weight intervals.
// This assumes runWeights values represent fractions or relative weights normalized to sum to 1.
for (int i = 0; i < nevents_to_process; i++) {
double randomNumber = randomDistribution(generator);
double randomNumber = randomDistribution(generator) * totalWeight;

double cumulativeWeight = 0;
for (const auto& weight : runWeights) {
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