34 lines
2.1 KiB
Markdown
34 lines
2.1 KiB
Markdown
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# fb_arc_set
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The aim of these 2 modules is to implement an algorithm which removes cycles in a directed graph by removing the least edges possible.
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A set of edges which must be removed to make a graph acyclic is also called a feedback arc set; and the
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set with the least edges is a minimal feedback arc set.
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## Algorithm
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A simple randomized algorithm for this problem generates a feedback arc set by executing following steps:
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* Order the vertices of the graph randomly, i.e. generate a random permutation of the set of vertices.
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* Select all edges ( u, v ) for which u > v in the ordering. These edges form a feedback arc set.
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## generator
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The generator program takes a graph as input. The program repeatedly generates a random solution
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to the problem as described above and writes its result to a circular buffer. It repeats this procedure until it is notified by the supervisor to terminate.
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SYNOPSIS
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generator EDGE1...
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EXAMPLE
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generator 0-1 1-2 1-3 1-4 2-4 3-6 4-3 4-5 6-0
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## supervisor
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The supervisor sets up the shared memory and the semaphores and initializes the circular buffer required
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for the communication with the generators. It then waits for the generators to write solutions to the
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circular buffer.
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The supervisor program takes no arguments.
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Once initialization is complete, the supervisor reads the solutions from the circular buffer and remem-
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bers the best solution so far, i.e. the solution with the least edges. Every time a better solution than the previous best solution is found, the supervisor writes the new solution to standard output. If a generator writes a solution with 0 edges to the circular buffer, then the graph is acyclic and the supervisor terminates. Otherwise the supervisor keeps reading results from the circular buffer until it receives a `SIGINT` or a `SIGTERM` signal.
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Before terminating, the supervisor notifies all generators that they should terminate as well. This can
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be done by setting a variable in the shared memory, which is checked by the generator processes before
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writing to the buffer. The supervisor then unlinks all shared resources and exits
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**Note: The description is from the task I got from TU.**
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