Simplify expand_t_blossom()
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107
cpp/mwmatching.h
107
cpp/mwmatching.h
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@ -1414,7 +1414,7 @@ public:
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assert(sub_blossom->vertex_dual_offset == 0);
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sub_blossom->vertex_dual_offset = vertex_dual_offset;
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// Add unlabeled blossom to the delta2 queue.
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// Add unlabeled sub-blossom to the delta2 queue.
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delta2_enable_blossom(sub_blossom);
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}
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@ -1423,65 +1423,53 @@ public:
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// that ran through this blossom by linking some of the sub-blossoms
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// into the tree.
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// Find the sub-blossom that was attached to the parent node
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// in the alternating tree.
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// Find the sub-blossom through which the expanding blossom was
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// attached to the alternating tree.
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BlossomT* entry = top_level_blossom(blossom->tree_edge.second);
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// Assign label T to that blossom and link to the alternating tree.
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assign_blossom_label_t(entry);
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entry->tree_edge = blossom->tree_edge;
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entry->tree_root = blossom->tree_root;
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// Find the position of this sub-blossom within the expanding blossom.
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auto subblossom_loc = blossom->find_subblossom(entry);
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VertexId entry_pos = subblossom_loc.first;
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auto entry_it = subblossom_loc.second;
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// Walk around the blossom from "entry" to the base
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// Get the edge that attaches this blossom to the alternating tree.
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VertexId x, y;
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std::tie(x, y) = blossom->tree_edge;
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// Walk around the expanding blossom from "entry" to its base
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// in an even number of steps.
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auto sub_begin = blossom->subblossoms.begin();
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auto sub_end = blossom->subblossoms.end();
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auto sub_it = entry_it;
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if (entry_pos % 2 == 0) {
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while ((sub_it != sub_begin) && (sub_it != sub_end)) {
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// Walk backward to the base.
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auto sub_begin = blossom->subblossoms.begin();
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while (sub_it != sub_begin) {
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// Assign label S to the next node on the path.
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// Assign label T to the current sub-blossom on the path.
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// This also assigns label S to the next sub-blossom.
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extend_tree_s_to_t(x, y);
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if (entry_pos % 2 == 0) {
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// Walk two steps backward to the base.
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--sub_it;
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extend_tree_t_to_s(sub_it->edge.first);
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// Assign label T to the next node on the path.
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assert(sub_it != sub_begin);
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--sub_it;
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BlossomT* sub_blossom = sub_it->blossom;
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assign_blossom_label_t(sub_blossom);
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sub_blossom->tree_edge = flip_vertex_pair(sub_it->edge);
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sub_blossom->tree_root = blossom->tree_root;
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}
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} else {
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// Walk forward to the base.
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auto sub_end = blossom->subblossoms.end();
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while (sub_it != sub_end) {
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// Assign label S to the next node on the path.
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extend_tree_t_to_s(sub_it->edge.second);
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// Get the edge from S-sub-blossom to next sub-blossom.
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std::tie(y, x) = sub_it->edge;
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} else {
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// Walk two steps forward to the base.
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++sub_it;
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// Assign label T to the next node on the path.
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// We may wrap past the end of the subblossom list.
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assert(sub_it != sub_end);
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VertexPair& tree_edge = sub_it->edge;
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// Get the edge from S-sub-blossom to next sub-blossom.
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std::tie(x, y) = sub_it->edge;
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++sub_it;
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BlossomT *sub_blossom = (sub_it == sub_end) ?
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blossom->subblossoms.front().blossom :
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sub_it->blossom;
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assign_blossom_label_t(sub_blossom);
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sub_blossom->tree_edge = tree_edge;
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sub_blossom->tree_root = blossom->tree_root;
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}
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}
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// Finally, assign label T to the base sub-blossom.
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BlossomT* base = blossom->subblossoms.front().blossom;
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assign_blossom_label_t(base);
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base->tree_edge = std::make_pair(x, y);
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base->tree_root = blossom->tree_root;
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// Delete the expanded blossom.
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nontrivial_blossom.erase(blossom->this_blossom_iterator);
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}
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@ -1655,34 +1643,6 @@ public:
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/* ********** Alternating tree: ********** */
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/**
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* Assign label S to the unlabeled blossom that contains vertex "x".
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*
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* The newly labeled S-blossom is added to the alternating tree
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* via its matched edge. All vertices in the newly labeled S-blossom
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* are added to the scan queue.
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*
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* @pre "x" is an unlabeled vertex.
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* @pre "x" is matched to a T-vertex via a tight edge.
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*/
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void extend_tree_t_to_s(VertexId x)
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{
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// Assign label S to the blossom that contains vertex "x".
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BlossomT* bx = top_level_blossom(x);
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assign_blossom_label_s(bx);
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// Vertex "x" is matched to T-vertex "y".
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VertexId y = vertex_mate[x];
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assert(y != NO_VERTEX);
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BlossomT* by = top_level_blossom(y);
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assert(by->label == LABEL_T);
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// Attach the blossom to the alternating tree via vertex "y".
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bx->tree_edge = std::make_pair(y, x);
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bx->tree_root = by->tree_root;
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}
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/**
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* Assign label T to the unlabeled blossom that contains vertex "y".
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*
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@ -1708,9 +1668,14 @@ public:
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by->tree_root = bx->tree_root;
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// Assign label S to the blossom that is mated to the T-blossom.
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VertexId z = vertex_mate[by->base_vertex];
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VertexId y2 = by->base_vertex;
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VertexId z = vertex_mate[y2];
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assert(z != NO_VERTEX);
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extend_tree_t_to_s(z);
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BlossomT* bz = top_level_blossom(z);
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assign_blossom_label_s(bz);
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bz->tree_edge = std::make_pair(y2, z);
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bz->tree_root = by->tree_root;
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}
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/**
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