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MapReduce >> mail # user >> Ant Colony Optimization for Travelling Salesman Problem in Hadoop


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Re: Ant Colony Optimization for Travelling Salesman Problem in Hadoop
Look at NShotInputFormat
call setNumberKeys to set the number of ants then
change the method getValueFromIndex to return the text representing the
original problem to each mapper -
what happens in the second and third jobs is an exercise but the saved test
needs to have pheremones and the original problem
On Fri, May 4, 2012 at 9:54 AM, sharat attupurath <[EMAIL PROTECTED]>wrote:

>  Hi,
>
> Thanks a lot for the quick reply sir! We are new to Apache Hadoop and
> haven't yet understood it properly yet. Can you please elaborate on how we
> can have multiple stages of mapreduce jobs for combining the trails as you
> have mentioned?
>
> We have been trying to find out how to write a custom splitter and almost
> all online resources tell to subclass the FileInputFormat and write only a
> custom RecordReader? Will it be possible to generate our splits in that way?
>
> Regards
>
> Sharat
>
> ------------------------------
> Date: Fri, 4 May 2012 09:22:51 -0700
> Subject: Re: Ant Colony Optimization for Travelling Salesman Problem in
> Hadoop
> From: [EMAIL PROTECTED]
> To: [EMAIL PROTECTED]
>
>
>
>
> On Fri, May 4, 2012 at 9:06 AM, sharat attupurath <[EMAIL PROTECTED]>wrote:
>
>  Hi,
>
> We are trying to parallelize the ant colony optimization algorithm for TSP
> over hadoop and are facing some issues. We are using TSPLIB as input files.
> The input is a text file containing eucledian coordinates of the cities -
> first column is city number and the next two columns contain the x and y
> coordinates respectively.
>
> What we intend to do is to take input from this single file, send copies
> of it to multiple mappers (each mapper acts like the ant in the algorithm),
> each mapper works on its input to find its own TSP solution that it outputs
> and finally the reducer outputs the smallest tour found by the mappers.
> Hope we are in the right track. Here are the issues:
>
> 1) Since the input file is small, we need to force hadoop to fire up
> multiple map tasks by replicating the input. How can we make an InputSplit
> of the whole file and replicate it so that the input can be sent to
> multiple mappers?
>
> Write a custom splitter sending the same data to all mappers - the only
> critical criteria is the number of "Ants"
>
>
> 2) the algorithm uses a shared pheromone array and each mapper needs to
> read and write data from this. How can we share the pheromone data across
> the mappers.
>
> You cannot share data across mappers and should not attempt to do so -
> Better to use the reducer(s) to combine trails  combine first pass trails
> and
> then pass the combined trails to another mapreduce job - this with the
> original problem plus the current pheremone trails
>
>
> Hope the questions are clear enough. Any help would be greatly
> appreciated.
>
> Thank you
>
> Regards
>
> Sharat
>
>
>
>
> --
> Steven M. Lewis PhD
> 4221 105th Ave NE
> Kirkland, WA 98033
> 206-384-1340 (cell)
> Skype lordjoe_com
>
>
>
--
Steven M. Lewis PhD
4221 105th Ave NE
Kirkland, WA 98033
206-384-1340 (cell)
Skype lordjoe_com