Tagged Questions

This is a mathematical structure composed of a set of points or vertices and a set of connectors or edges. The edges connect the vertices and those vertices are directed. Also no cycles or in other words a directed edge that connects a vertex to a vertex are disallowed.

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0
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0answers
48 views

Minimum Weight Ordering of nodes on a directed graph

I'm bumping my head against the wall trying to prove this problem is NP-complete (it might not be) Let $G = (V,E)$ be a directed graph with weights $w:E \to \mathbb{R_{\geq 0}}$ on the edges. The ...
4
votes
0answers
72 views

Indexing structure for all-pairs min-cuts in a huge DAG

I have a huge DAG - e.g., the dependency graph of all packages in a linux distribution. Suppose I'd like to make a user-friendly tool that makes it very easy to understand how to break the transitive ...
-2
votes
1answer
65 views

Practical topological sorting for dependency graphs [closed]

I have been reading the Wikipedia page on Topological Sorting, specifically the depth-first algorithm which also detects cycles while it is building the sort. But from some experimentation with this ...
-1
votes
1answer
139 views

All pairs shortest paths in a DAG [closed]

I have studied the Floyd-Warshall and Johnson algorithms. I am trying to understand if the all pairs shortest paths research in a directed graph G can be implemented in a more efficient way if I ...
4
votes
0answers
141 views

K-path cover problem for a DAG

I am doing a little literature review and I was trying to know if, for a directed acyclic graph, the minimum k-path cover problem is solvable in polynomial time. A k-path cover is a set of paths with ...
7
votes
1answer
116 views

Complexity of counting poset automorphisms

A (finite) poset $P = (X, <)$, or partially ordered set, is a (finite) set $X$ equipped with a transitive antisymmetric relation $<$; it can be equivalently seen as a DAG $G = (X, E)$ that is ...
-5
votes
1answer
197 views

Efficient algorithm to create a directed dependency graph

I am looking for an efficient algorithm to create a graph like this: Initially the graph is filled with x then hs then ...
4
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0answers
118 views

Deciding transitivity of a directed acyclic graph [duplicate]

Is there any algorithm that decides whether a given directed acyclic graph is transitive or not, in time-complexity asymptotically better than boolean matrix multiplication?
9
votes
5answers
494 views

Transitivity check vs. Transitive Closure

Is checking transitivity of a digraph not easier than (in terms of asymptotic complexity) taking the transitive closure of the digraph? Do we know any lower bound better than $\Omega(n^2)$ to ...
3
votes
1answer
202 views

Maximize the expected number of “losers” - Is it NP-hard?

I am trying to find a reduction for a problem that seems NP-hard: Let me start from a toy example. Consider 3 elements, $a$, $b$, and $c$. You want to choose two pairs out of the three pairs and ...
1
vote
1answer
124 views

How to find the set of edges for the directed graph associated with a partial order?

I have a set $S$, and a partial order relation $\preceq$ defined on $S$. The way this partial order is given to me is through a function $f:S\times S \to \{true, false\}$, where $f(a,b) = true$ if ...
11
votes
3answers
468 views

Complexity of topological sort with constrained positions

I am given as input a DAG $G$ of $n$ vertices where each vertex $x$ is additionally labeled with some $S(x) \subseteq \{1, \ldots, n\}$. A topological sort of $G$ is a bijection $f$ from the vertices ...
9
votes
1answer
258 views

Finding optimal parallelization from general weighted undirected graph

I am solving a problem of "blending" sets of overlapping images. These sets can be represented by undirected weighted graph such as this one: Each node represents an image. Overlapping images are ...
6
votes
0answers
300 views

Partitioning DAG into Paths

What bounds (lower or upper) are known about the complexity of partitioning a Directly Acyclic Graph (DAG) into paths of respective sizes $n_1,\ldots,n_w$, such that to minimize their entropy $n{\cal ...
3
votes
0answers
397 views

Lowest Common Ancestor Problem in Directed Acyclic Graphs

What is the current best bound for the following problem in DAG: "For any pair of vertices in a given graph G, return all the LCAs of the same"? Edit: I am working on all-pair reachability problem in ...
4
votes
1answer
409 views

Multiple-sources dominator trees: compact representation and fast algorithm?

I recently learnt about the concept of dominator trees and was fascinated by it. I was wondering how the problem extends to computing dominators from multiple sources, or even from all vertices in ...
3
votes
0answers
235 views

Dynamic shortest path data structure for DAG

Let $G$ be a dynamic DAG (directed acyclic graph) where new vertices and new edges can be inserted. I am looking for an efficient data structure/algorithm to maintain the shortest path from a fixed ...
5
votes
1answer
160 views

Canonical labeling of special classes of DAGs

Graph Isomorphism of directed acyclic graphs (DAGs) is known to be GI-complete. So a polynomial time algorithm to canonize DAGs is not known. What are some special classes of DAGs that can be ...
3
votes
1answer
248 views

Breadth first search and Eppstein K shortest paths algorithm

I'm trying to understand the algorithm for finding K shortest paths in a graph described by Eppstein in this paper: http://www.ics.uci.edu/~eppstein/pubs/Epp-SJC-98.pdf I have trouble particularly ...
5
votes
1answer
196 views

Revision Tracking Graph

Define the Revision Tracking Graph (RTG), which is an oriented graph (without circles) where each node x has a set C(x) associated with it. C(x) contains all edges on all paths from a node 0 ( C(0) = ...
24
votes
0answers
975 views

Combinatorics of Bellman-Ford or how to make cyclic graphs acyclic?

Roughly speaking, my question is: How costly is to make a cyclic graph acyclic while preserving all simple $s$-$t$ paths? Let $K_n$ be a complete undirected graph on vertices $\{0,1,\ldots,n+1\}$. ...
14
votes
1answer
490 views

Exact Algorithm for edge labeling problem in DAG

I am implementing some system part of which requires some help. I am therefore framing it as a graph problem to make it domain independent. Problem: We are given directed acyclic graph $G=(V,E)$. ...
13
votes
1answer
1k views

Finding k shortest Paths with Eppstein's Algorithm

I'm trying to figure out how the Path Graph $P(G)$ according to Eppstein's Algorithm in this paper works and how I can reconstruct the $k$ shortest paths from $s$ to $t$ with the corresponding heap ...
11
votes
3answers
380 views

Efficient DAG comparison over a network

In distributed version control systems (such a Mercurial and Git) there is a need to efficiently compare directed acyclic graphs (DAGs). I'm a Mercurial developer, and we would be very interested in ...
2
votes
0answers
294 views

Recursive parallel topological sorting in linear time

While doing some research on topological sorting I came across a paper Parallel Topological Sorting Algorithm, TADA, A. and MIGITA, M. and NAKAMURA, R. which claims a recursive divide-and-conquer ...
0
votes
0answers
421 views

Cycles in a directed graph

Wondering if we can prove the following or if it is already proved where can I get the proof. Let $v_1, v_2, v_3, \ldots, v_n$ and $t$ be $n+1$ vertexes in a directed graph. $v_1, v_2, v_3, \ldots, ...
3
votes
1answer
308 views

measures for a DAG (directed acyclic graph)?

Recently, I want to devise some kernelization (in the framework of parameterized complexity) for problem on DAG. So, find a proper parameter is essential. Well, is there a measure for the importance ...
3
votes
1answer
201 views

Shortest path in a DAG consisting of multiple copies of a smaller DAG

Let's say we have $k$ weighted DAGs (directed acyclic graphs) $$H_1 = (V_1, A_1), \dots, H_k = (V_k, A_k)$$ that are copies of one another. Now consider another weighted DAG $G$ that is built by ...
6
votes
0answers
200 views

Restricted Reachability Problem

Let $G$ be a directed acyclic graph with $V$ vertices and $E$ edges. Choose some subset of $n\leq V$ "special" vertices $\{v_i\}_{i=1}^n$. How efficiently can we preprocess $(G, \{v_i\})$ so that we ...
3
votes
3answers
512 views

A possibly new representation of DAGs

I had an idea for a way of representing DAGs, it's very easy to explain: Each node in the DAG is given an array of n integers. If it is possible to traverse from A to B then each of B's integers must ...
3
votes
1answer
275 views

Finding common label sequences in a directed acyclic graph

I have a directed acyclic graph with ~250k nodes, each node has one of about 100 symbols as label. Letting a word be the sequence of n symbols that corresponds to a path containing n nodes in the ...
16
votes
2answers
329 views

Does an algorithm exist to efficiently maintain connectedness information for a DAG in presence of inserts/deletes?

Given a directed acyclic graph, $G(V,E)$, is it possible to efficiently support the following operations? $isConnected(G,a,b)$: Determines if there is a path in $G$ from node $a$ to node $b$ ...
4
votes
2answers
212 views

Generation of unlabeled acyclic digraphs

I'm looking for an algorithm to efficiently generate all unlabeled acyclic digraphs of a given order. (By "unlabeled" I mean that no two of the generated digraphs should be isomorphic.) Thanks Edit: ...
8
votes
3answers
513 views

Route existence between n pairs of nodes

Given a directed acyclic graph with $2n$ nodes how can one determine if there is a path between any of following n pairs of nodes $(1 \rightarrow n+1), \ldots, (n \rightarrow n+n)$? There is a simple ...
8
votes
2answers
786 views

Testing/Identifying a Topological Sorting

You're given a set of $n$ Directed Acyclic Graphs $G_1, G_2, ..., G_n$ over the same set of $m$ vertices $V$. You're also given a permutation of the set of vertices $(v_1,v_2,...,v_m)$. What is the ...
-4
votes
1answer
399 views

Compact representation of DAG,

Given a DAG (which represents DDG – each node is a operation the in-edge/s show the operands from which inputs are taken) I want to obtain its compact representation of the graph, in such a way that: ...
1
vote
2answers
156 views

Special Properties Of DAWGs with Unique Elements

A DAWG is a specialized form of a Directed Acyclic Graph. Admittedly, not terribly specialized. I was wondering if DAWGs built from proper sets (unique, sorted) had any special properties? It seems ...
6
votes
3answers
1k views

Number of reachable vertices in DAG for every vertex

Let $G(V,E)$ be an acyclic directed graph, such that out-degree of any vertex is $O(\log{|V|})$. For every vertex of $G$ we can count the number of reachable vertices, just by running dfs from every ...
1
vote
0answers
1k views

DAG partitioning to subgraphs

Given a DAG with $|V| = n$ and has $s$ sources, we have to present subgraphs such that each subgraph has approximately $k_1=\sqrt{s}$ sources and approximately $k_2=\sqrt{n}$ nodes. (Note: ...
11
votes
4answers
641 views

Directed NP-hard problems on DAGs

Tree width measures how close a graph is to a tree. Several NP-hard problems are tractable on graphs with bounded tree width. If a problem remains NP-hard on trees then tree width cannot save us. This ...
12
votes
1answer
516 views

Positive topological ordering, take 2

This is a followup to David Eppstein's recent question and is motivated by the same problems. Suppose I have a dag with real-number weights on its vertices. Initially, all of the vertices are ...
40
votes
5answers
2k views

Positive topological ordering

Suppose I have a directed acyclic graph with real-number weights on its vertices. I want to find a topological ordering of the DAG in which, for every prefix of the topological ordering, the sum of ...
29
votes
3answers
1k views

Given a weighted dag, is there an O(V+E) algorithm to replace each weight with the sum of its ancestor weights?

The problem, of course, is double counting. It's easy enough to do for certain classes of DAGs = a tree, or even a serial-parallel tree. The only algorithm I have found which works on general DAGs in ...