-
Notifications
You must be signed in to change notification settings - Fork 121
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
- Loading branch information
Showing
4 changed files
with
148 additions
and
135 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
133 changes: 133 additions & 0 deletions
133
include/random_walks/accelerated_billiard_walk_utils.hpp
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,133 @@ | ||
| // VolEsti (volume computation and sampling library) | ||
|
|
||
| // Copyright (c) 2012-2020 Vissarion Fisikopoulos | ||
| // Copyright (c) 2018-2020 Apostolos Chalkis | ||
| // Copyright (c) 2024 Luca Perju | ||
|
|
||
| // Licensed under GNU LGPL.3, see LICENCE file | ||
|
|
||
| #ifndef ACCELERATED_BILLIARD_WALK_UTILS_HPP | ||
| #define ACCELERATED_BILLIARD_WALK_UTILS_HPP | ||
|
|
||
| #include <Eigen/Eigen> | ||
| #include <vector> | ||
|
|
||
| const double eps = 1e-10; | ||
|
|
||
| // data structure which maintains the values of (b - Ar)/Av, and can extract the minimum positive value and the facet associated with it | ||
| // vec[i].first contains the value of (b(i) - Ar(i))/Av(i) + moved_dist, where moved_dist is the total distance that the point has travelled so far | ||
| // The heap will only contain the values from vec which are greater than moved_dist (so that they are positive) | ||
| template<typename NT> | ||
| class BoundaryOracleHeap { | ||
| public: | ||
| int n, heap_size; | ||
| std::vector<std::pair<NT, int>> heap; | ||
| std::vector<std::pair<NT, int>> vec; | ||
|
|
||
| private: | ||
| int siftDown(int index) { | ||
| while((index << 1) + 1 < heap_size) { | ||
| int child = (index << 1) + 1; | ||
| if(child + 1 < heap_size && heap[child + 1].first < heap[child].first - eps) { | ||
| child += 1; | ||
| } | ||
| if(heap[child].first < heap[index].first - eps) | ||
| { | ||
| std::swap(heap[child], heap[index]); | ||
| std::swap(vec[heap[child].second].second, vec[heap[index].second].second); | ||
| index = child; | ||
| } else { | ||
| return index; | ||
| } | ||
| } | ||
| return index; | ||
| } | ||
|
|
||
| int siftUp(int index) { | ||
| while(index > 0 && heap[(index - 1) >> 1].first - eps > heap[index].first) { | ||
| std::swap(heap[(index - 1) >> 1], heap[index]); | ||
| std::swap(vec[heap[(index - 1) >> 1].second].second, vec[heap[index].second].second); | ||
| index = (index - 1) >> 1; | ||
| } | ||
| return index; | ||
| } | ||
|
|
||
| // takes the index of a facet, and (in case it is in the heap) removes it from the heap. | ||
| void remove (int index) { | ||
| index = vec[index].second; | ||
| if(index == -1) { | ||
| return; | ||
| } | ||
| std::swap(heap[heap_size - 1], heap[index]); | ||
| std::swap(vec[heap[heap_size - 1].second].second, vec[heap[index].second].second); | ||
| vec[heap[heap_size - 1].second].second = -1; | ||
| heap_size -= 1; | ||
| index = siftDown(index); | ||
| siftUp(index); | ||
| } | ||
|
|
||
| // inserts a new value into the heap, with its associated facet | ||
| void insert (const std::pair<NT, int> val) { | ||
| vec[val.second].second = heap_size; | ||
| vec[val.second].first = val.first; | ||
| heap[heap_size++] = val; | ||
| siftUp(heap_size - 1); | ||
| } | ||
|
|
||
| public: | ||
| BoundaryOracleHeap() {} | ||
|
|
||
| BoundaryOracleHeap(int n) : n(n), heap_size(0) { | ||
| heap.resize(n); | ||
| vec.resize(n); | ||
| } | ||
|
|
||
| // rebuilds the heap with the existing values from vec | ||
| // O(n) | ||
| void rebuild (const NT &moved_dist) { | ||
| heap_size = 0; | ||
| for(int i = 0; i < n; ++i) { | ||
| vec[i].second = -1; | ||
| if(vec[i].first - eps > moved_dist) { | ||
| vec[i].second = heap_size; | ||
| heap[heap_size++] = {vec[i].first, i}; | ||
| } | ||
| } | ||
| for(int i = heap_size - 1; i >= 0; --i) { | ||
| siftDown(i); | ||
| } | ||
| } | ||
|
|
||
| // returns (b(i) - Ar(i))/Av(i) + moved_dist | ||
| // O(1) | ||
| NT get_val (const int &index) { | ||
| return vec[index].first; | ||
| } | ||
|
|
||
| // returns the nearest facet | ||
| // O(1) | ||
| std::pair<NT, int> get_min () { | ||
| return heap[0]; | ||
| } | ||
|
|
||
| // changes the stored value for a given facet, and updates the heap accordingly | ||
| // O(logn) | ||
| void change_val(const int& index, const NT& new_val, const NT& moved_dist) { | ||
| if(new_val < moved_dist - eps) { | ||
| vec[index].first = new_val; | ||
| remove(index); | ||
| } else { | ||
| if(vec[index].second == -1) { | ||
| insert({new_val, index}); | ||
| } else { | ||
| heap[vec[index].second].first = new_val; | ||
| vec[index].first = new_val; | ||
| siftDown(vec[index].second); | ||
| siftUp(vec[index].second); | ||
| } | ||
| } | ||
| } | ||
| }; | ||
|
|
||
|
|
||
| #endif |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters