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update doc string in BayesTreeMarginalizationHelper.h

release/4.3a0
Jeffrey 2024-10-29 15:13:09 +08:00
parent 896e52ca27
commit c6ba2b5fd8
1 changed files with 23 additions and 41 deletions
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64
gtsam_unstable/nonlinear/BayesTreeMarginalizationHelper.h
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@ -37,53 +37,33 @@ public:
using Clique = typename BayesTree::Clique;
using sharedClique = typename BayesTree::sharedClique;
/** Get the additional keys that need to be re-eliminated when marginalizing
/** Get the additional keys that need reelimination when marginalizing
* the variables in @p marginalizableKeys from the Bayes tree @p bayesTree.
*
* @param[in] bayesTree The Bayes tree to be marginalized.
* @param[in] bayesTree The Bayes tree.
* @param[in] marginalizableKeys The keys to be marginalized.
*
*
* When marginalizing a variable @f$ \theta @f$ in a Bayes tree, some nodes
* may need to be re-eliminated. The variable to be marginalized should be
* eliminated first.
* When marginalizing a variable @f$ \theta @f$ from a Bayes tree, some
* nodes may need reelimination to ensure the variables to marginalize
* be eliminated first.
*
* 1. If @f$ \theta @f$ is already in a leaf node @f$ L @f$, and all other
* frontal variables within @f$ L @f$ are to be marginalized, then this
* node does not need to be re-eliminated; the entire node can be directly
* marginalized.
* We should consider two cases:
*
* 2. If @f$ \theta @f$ is in a leaf node @f$ L @f$, but @f$ L @f$ contains
* other frontal variables that do not need to be marginalized:
* a. If all other non-marginalized frontal variables are listed after
* @f$ \theta @f$ (each node contains a frontal list, with variables to
* be eliminated earlier in the list), then node @f$ L @f$ does not
* need to be re-eliminated.
* b. Otherwise, if there are non-marginalized nodes listed before
* @f$ \theta @f$, then node @f$ L @f$ needs to be re-eliminated, and
* correspondingly, all nodes between @f$ L @f$ and the root need to be
* re-eliminated.
* 1. If a child node relies on @f$ \theta @f$ (i.e., @f$ \theta @f$
* is a parent / separator of the node), then the frontal
* variables of the child node need to be reeliminated. In
* addition, all the descendants of the child node also need to
* be reeliminated.
*
* 3. If @f$ \theta @f$ is in an intermediate node @f$ M @f$ (non-leaf node),
* but none of @f$ M @f$'s child nodes depend on variable @f$ \theta @f$
* (they only depend on other variables within @f$ M @f$), then during the
* process of marginalizing @f$ \theta @f$, @f$ M @f$ can be treated as a
* leaf node, and @f$ M @f$ should be processed following the same
* approach as for leaf nodes.
* 2. If other frontal variables in the same node with @f$ \theta @f$
* are in front of @f$ \theta @f$ but not to be marginalized, then
* these variables also need to be reeliminated.
*
* In this case, the original elimination of @f$ \theta @f$ does not
* depend on the elimination results of variables in the child nodes.
* These variables were eliminated before @f$ \theta @f$ in the original
* Bayes tree, and after reelimination they will be eliminated after
* @f$ \theta @f$ so that @f$ \theta @f$ can be marginalized safely.
*
* 4. If @f$ \theta @f$ is in an intermediate node @f$ M @f$ (non-leaf node),
* and there exist child nodes that depend on variable @f$ \theta @f$,
* then not only does node @f$ M @f$ need to be re-eliminated, but all
* child nodes dependent on @f$ \theta @f$, including descendant nodes
* recursively dependent on @f$ \theta @f$, also need to be re-eliminated.
*
* The frontal variables in child nodes were originally eliminated before
* @f$ \theta @f$ and their elimination results are relied upon by
* @f$ \theta @f$'s elimination. When re-eliminating, they should be
* eliminated after @f$ \theta @f$.
*/
static void gatherAdditionalKeysToReEliminate(
const BayesTree& bayesTree,
@ -102,20 +82,21 @@ public:
}
checkedCliques.insert(clique);
bool is_leaf = clique->children.empty();
bool need_reeliminate = false;
bool has_non_marginalizable_ahead = false;
for (Key i: clique->conditional()->frontals()) {
if (marginalizableKeySet.count(i)) {
if (has_non_marginalizable_ahead) {
// Case 2 in the docstring
need_reeliminate = true;
break;
} else {
// Check whether there're child nodes dependent on this key.
// Check whether there's a child node dependent on this key.
for(const sharedClique& child: clique->children) {
if (std::find(child->conditional()->beginParents(),
child->conditional()->endParents(), i)
!= child->conditional()->endParents()) {
// Case 1 in the docstring
need_reeliminate = true;
break;
}
@ -127,10 +108,11 @@ public:
}
if (!need_reeliminate) {
// No variable needs to be reeliminated
continue;
} else {
// need to re-eliminate this clique and all its children that depend on
// a marginalizable key
// Need to reeliminate the current clique and all its children
// that rely on a marginalizable key.
for (Key i: clique->conditional()->frontals()) {
additionalKeys.insert(i);
for (const sharedClique& child: clique->children) {