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add explanatory comments

release/4.3a0
Varun Agrawal 2025-01-28 22:08:17 -05:00
parent 2702854c18
commit 2e4ae8ca0a
1 changed files with 5 additions and 1 deletions
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6
gtsam/discrete/DiscreteFactorGraph.cpp
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@ -215,6 +215,7 @@ namespace gtsam {
EliminateDiscrete(const DiscreteFactorGraph& factors, EliminateDiscrete(const DiscreteFactorGraph& factors,
const Ordering& frontalKeys) { const Ordering& frontalKeys) {
gttic(product); gttic(product);
// `product` is scaled later to prevent underflow.
DiscreteFactor::shared_ptr product = factors.product(); DiscreteFactor::shared_ptr product = factors.product();
gttoc(product); gttoc(product);
@ -222,8 +223,11 @@ namespace gtsam {
gttic(sum); gttic(sum);
DiscreteFactor::shared_ptr sum = product->sum(frontalKeys); DiscreteFactor::shared_ptr sum = product->sum(frontalKeys);
gttoc(sum); gttoc(sum);
// Normalize/scale to prevent underflow. // Normalize/scale to prevent underflow.
// We divide both `product` and `sum` by `max(sum)`
// since it is faster to compute and when the conditional
// is formed by `product/sum`, the scaling term cancels out.
gttic(scale); gttic(scale);
DiscreteFactor::shared_ptr denominator = sum->max(sum->size()); DiscreteFactor::shared_ptr denominator = sum->max(sum->size());
product = product->operator/(denominator); product = product->operator/(denominator);