# R igraph manual pages

Use this if you are using igraph from R

 feedback_arc_set {igraph} R Documentation

## Finding a feedback arc set in a graph

### Description

A feedback arc set of a graph is a subset of edges whose removal breaks all cycles in the graph.

### Usage

``````feedback_arc_set(graph, weights = NULL, algo = c("approx_eades", "exact_ip"))
``````

### Arguments

 `graph` The input graph `weights` Potential edge weights. If the graph has an edge attribute called ‘`weight`’, and this argument is `NULL`, then the edge attribute is used automatically. The goal of the feedback arc set problem is to find a feedback arc set with the smallest total weight. `algo` Specifies the algorithm to use. “`exact_ip`” solves the feedback arc set problem with an exact integer programming algorithm that guarantees that the total weight of the removed edges is as small as possible. “`approx_eades`” uses a fast (linear-time) approximation algorithm from Eades, Lin and Smyth. “`exact`” is an alias to “`exact_ip`” while “`approx`” is an alias to “`approx_eades`”.

### Details

Feedback arc sets are typically used in directed graphs. The removal of a feedback arc set of a directed graph ensures that the remaining graph is a directed acyclic graph (DAG). For undirected graphs, the removal of a feedback arc set ensures that the remaining graph is a forest (i.e. every connected component is a tree).

### Value

An edge sequence (by default, but see the `return.vs.es` option of `igraph_options`) containing the feedback arc set.

### References

Peter Eades, Xuemin Lin and W.F.Smyth: A fast and effective heuristic for the feedback arc set problem. Information Processing Letters 47:6, pp. 319-323, 1993

### Examples

``````
g <- sample_gnm(20, 40, directed=TRUE)
feedback_arc_set(g)
feedback_arc_set(g, algo="approx")
``````

[Package igraph version 1.3.2 Index]