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LEDA

LEDA. A Library of Efficient Data-Types and Algorithms. http://www.algorithmic-solutions.com/enleda.htm. Presentation by Amitai Armon. Example: Planarity Testing. #include <LEDA/graph_alg.h> using namespace leda; int main(int argc, char * argv[]) { graph G; string filename(argv[1]);

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LEDA

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  1. LEDA A Library of Efficient Data-Types and Algorithms http://www.algorithmic-solutions.com/enleda.htm Presentation by Amitai Armon

  2. Example: Planarity Testing #include <LEDA/graph_alg.h> using namespace leda; int main(int argc, char * argv[]) { graph G; string filename(argv[1]); G.read(filename); cout << PLANAR(G) << endl; }

  3. Topics • What is LEDA? • What does it include? • LEDA data structures examples • LEDA graphs • Compiling with LEDA • Where to find more info

  4. What is LEDA • A C++ library of data-types and algorithms • Includes dozens of classes, developed over more than 15 years (Naher & Mehlhorn) • Works cross-platform • Extensively tested • Efficient • Extensively documented (manual, guide, book) • Installed in more than 3000 sites.

  5. A note about efficiency • LEDA code is likely to be more efficient than the first implementation of most users • It is also more efficient than STL in many cases • …but it is not magical: • The right DS should be used (e.g. dynamic graph vs. static graph, array vs. dictionary) • Robustness damages efficiency, so if efficiency is an issue, check if LEDA creates bottlenecks and should be replaced by platform/application optimized code.

  6. LEDA Contents • Basic data structures: lists, queues, stacks, arrays, sets, etc. • Advanced data structures: e.g. dictionary, partition, priority queues (with Fibonacci heaps), dynamic trees, and more. • Graphs: Data-types, generators, iterators, and algorithms - including BFS, DFS, MST, Max-Flow, Min-Cost-Flow, Min-Cut, Matchings, Planarity-testing, Triangulation, Five-Colors,…

  7. LEDA Contents – continued • Linear algebra & number theory: matrices, modular arithmetic, integers of arbitrary length, numeric functions… • Lossless compression coders (Huffman, LZ…) • Geometrictypes & algorithms. (e.g. circle, sphere, triangulation, convex hull…) • Graphics: windows, menus, graph-window • Simple data types and support functions: strings, tuples, random-variables, I/O, etc.

  8. LEDA Extensions 12 packages, including: • Curve reconstruction Algorithms • K-cut (approximation) • Minimum Mean cycle • D-dimensional Geometry • Dynamic Graph algorithms • And more

  9. A DS Example: Dynamic Trees #include < LEDA/dynamic_trees.h > dynamic_trees D vertex D.make(void* x=nil) void D.link(vertex v, vertex w, double x, void* e_inf=nil) void D.update(vertex v, double x) vertex D.mincost(vertex v) double D.cut(vertex v) vertex D.lca(vertex v, vertex w) void* D.vertex_inf(vertex v), void* D.edge_inf(vertex(v) • O(log2n) expected amortized time per operation

  10. A DS Example: Dynamic Trees #include < LEDA/dynamic_trees.h > dynamic_trees D vertex D.make(void* x=nil) void D.link(vertex v, vertex w, double x, void* e_inf=nil) void D.update(vertex v, double x) vertex D.mincost(vertex v) double D.cut(vertex v) vertex D.lca(vertex v, vertex w) void* D.vertex_inf(vertex v), void* D.edge_inf(vertex(v) • O(log2n) expected amortized time per operation

  11. A DS Example: Dynamic Trees #include < LEDA/dynamic_trees.h > dynamic_trees D vertex D.make(void* x=nil) void D.link(vertex v, vertex w, double x, void* e_inf=nil) void D.update(vertex v, double x) vertex D.mincost(vertex v) double D.cut(vertex v) vertex D.lca(vertex v, vertex w) void* D.vertex_inf(vertex v), void* D.edge_inf(vertex(v) • O(log2n) expected amortized time per operation

  12. A DS Example: Lists • #include < LEDA/list.h > list <E> L – creates a list of items with information of type E. E.g.: list<int>, list<string>, list<edge>, etc. • Operations: push(E item), append, pop, reverse, size, sort, unique, max, head, tail, succ, pred, print, forall(x, L), etc. • List access returns a list_item object (‘pointer to element’). Its information can be found only in the list itself. For example: list_item lowest=L.min(); cout << L[lowest];

  13. A DS Example - contd. • For a proof of non-planarity we supply an empty list of edges: list<edge> edge_list; if (PLANAR(G, edge_list)==0) forall (x,edge_list) G.print_edge(x); • List is implemented by a doubly linked list (use slist<E> for a singly-linked list). • Templates and the items concept are used in most of LEDA’s DSs, including stack<E>, queue<E>, array<E>, array2<E>, set<E>, and others.

  14. raphs in LEDA

  15. The graph/ugraph Classes • Represent directed/undirected graphs • Allow lots of graph operations: Adding/removing nodes/edges, node/edge iteration and sorting, computing and iterating faces, and more. • Persistent – can be read/written from/into a file • Has lots of implemented algorithms

  16. Creating a new graph • First option: start with an empty graph and update it graph G; // Initializes an empty directed graph ugraph G; // Initializes an empty undirected graph node G.new_node(); // New node is returned edge G.new_edge(node v, node w) => A lot of work!

  17. Creating a new graph - easier Use the generators for various graph types: • void random_graph(graph& G, int n, int m) • void random_graph(graph& G, int n, double p) • void random_simple_graph(graph& G, int n, int m) • void complete_graph(graph& G, int n) • random_bigraph – for a bipartite graph • random_planar_graph • And more

  18. Creating a new graph – from file • int G.read(string filename) (returns 0 if OK) void G.read(istream& I = cin) void G.write(ostream& O = cout) void G.write(string filename) • File format is simple: textual description, with each edge/node in a different line • Can also read another standard format, GML, with read_gml, etc.

  19. Nodes/Edges Iteration • forall_nodes(v, G) (The nodes of G are successively assigned to v) • forall_edges(e, G) • forall_adj_nodes(v, w) • forall_adj_edges(e, w) • forall_out_edges(e, w) • forall_in_edges(e, w) • etc…

  20. Node and Edge Data Structures • Node/edge arrays: The index to the array is a node/edge Construction: node_array<T> A(graph G) Access/assignment: T& A[node v] • Similarly we have node/edge lists, sets, maps, priority queues. They are optimized for nodes/edges.

  21. Introducing Weights • The class GRAPH<vtype, etype> includes information of the specified types for each vertex and node. E.g.: GRAPH<int, int> G; • Some useful functionality: node G.new_node(vtype x) edge G.new_edge(node v, node w, etype x) void G.assign(edge e, etype x) etype G.inf(edge e) edge_array<etype>& G.edge_data() • A parameterized GRAPH may be used wherever a graph may be used. • It can be read/written from/to a file with all the information.

  22. Graph Algorithms • Include: BFS, DFS, MST, Dijkstra, Bellman-Ford, Max-Flow, Min-Cost-Flow, Min-Cut, Matchings, Planarity-testing, Triangulation, Five-Colors,… • Can be included all at once: <LEDA/graph_alg.h> • Examples: • void DIJKSTRA_T(graph G, node s, edge_array<NT> cost, node_array<NT>& dist, node_array<edge>& pred) • list<node> MIN_CUT(graph G, edge_array<int> weight) • list<node> BFS(graph G, node s, node_array<int>& dist, node_array<edge>& pred) • list<edge> DFS_NUM(graph G, node_array<int>& dfsnum, node_array<int>& compnum)

  23. Graph Window • A powerful interactive graphic interface for graph operations and editing. • Can perform anything that can be done through a program, and has many customization options. • Basic operations: • GraphWin gw(graph& G, const char* win_label="") • gw.display() • Gw.edit() • More details in the LEDA website.

  24. Graph Window - Screenshots

  25. Semi-Dynamic Graphs • The graph class allows dynamic graph changes, but in most applications the graph doesn’t change after construction. • Semi-dynamic graphs are an alternative implementation of graphs, in which upper bounds on n and m may be supplied, in order to get better performance: graph G; void G.init(int n, int m); • Requires compilation with -DGRAPH_REP=2

  26. Static Graphs • May not change at all after their construction. • Significantly more efficient. We use: void G.start_construction(int n, int m) void G.finish_construction() • Slots: more efficient ways for associating data with nodes/edges (compared to node/edge arrays). • But: this is an experimental class with limited functionality compared to semi-dynamic graphs or ordinary graphs.

  27. Compiling with LEDA • We have LEDA version 4.4 for the following platforms: • Linux: Redhat 7.0 with g++ 2.96 • Linux: Redhat 8.0 with g++ 3.2 Both are installed in the TAU CS network • Windows with Visual C++ 6.0 • Windows with Visual C++ 7.0 (.Net) Both can be installed from CD on a PC

  28. Compiling with LEDA: Libraries The LEDA library is actually divided into 7 libraries: • Most of LEDA is in libL • Graphs and related data type are in libG • The alternative semi-dynamic implementation is in libG2 • libP- Geometry in the plane • libW – Graphics such as window and GraphWin • libD3 – 3D geometry • libGeoW – Visualizing sets of geometric objects

  29. Compiling with LEDA: Includes • Naturally, all the classes we use should be included (explicitly or by other includes). • LEDA types are in namespace leda (prefix leda::), in order to prevent ambiguity. • If ambiguity is not an issue – write: using namespace leda; and then you don’t have to add leda::

  30. Compiling with LEDA: CS Linux • Write the following line in your xterm: setenv LEDAROOT /usr/local/lib/LEDA-4.4-complete-i386-linux-redhat-7.0-g++-2.96/ Or, with Redhat 8.0: setenv LEDAROOT /usr/local/lib/LEDA-4.4-complete-i386-linux-redhat-8.0-g++-3.2/ - It is recommended to append the above line to your .login file.

  31. Compiling with LEDA: CS Linux Makefile example: Is_planar : Is_planar.o /usr/bin/g++ -Wall -O2 -L$(LEDAROOT) -o Is_planar Is_planar.o -lL -lG Is_planar.o: Is_planar.c /usr/bin/g++ -I$(LEDAROOT)/incl -O2 -c -o Is_planar.o Is_planar.c • Graphwin requires –lW -lP –lG –lL –lX11 –L/usr/X11R6/lib/

  32. Compiling with LEDA: Windows • Install the library for the appropriate compiler version from the CD (after signing a non-distribution form). • Open the supplied sample workspace. • Adjust the include and lib dirs in VS. • Add your LEDA directory to the PATH environment variable. • Elaborate instructions are in the LEDA website.

  33. Documentation • The LEDA website includes a user manual, describing all the LEDA classes, and a user guide, with examples and tips. http://www.algorithmic-solutions.com/enleda.htm • The LEDA book, by Mehlhorn and Naher, can be found at the library, and is also available on-line at the LEDA website.

  34. Conclusions • We’ve seen an overview of LEDA • It’s a useful and easy-to-use tool • Let’s use it…

  35. LEDA Questions?

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