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POHadoop Matrix Multiplication
 

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  1. POHadoop Matrix Multiplication
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    <p>I was running the MapReduce Matrix Multiplication program found at <a href="http://www.norstad.org/matrix-multiply/index.html" rel="nofollow">http://www.norstad.org/matrix-multiply/index.html</a>. I found out that this implementation doesn't work properly when there are 0's in the input matrices. But I don't understand why, and how do I modify the program to make it work? The MapReduce operation completes, but the output is always a matrix with all elements 0.</p> <p>My input Matrices A &amp; B are:</p> <pre><code>Matrix A Matrix B 0 0 0 6 7 4 0 1 6 9 1 3 7 8 9 7 6 2 </code></pre> <p>Output Matrix:</p> <pre><code>0 0 0 0 0 0 0 0 0 </code></pre> <p>The following are taken from the log files for the job:</p> <p>Map Output for matrixB:</p> <pre><code>##### Map setup: matrixA = false for hdfs://localhost/user/hadoop-user/B strategy = 4 R1 = 4 I = 3 K = 3 J = 3 IB = 3 KB = 3 JB = 3 ##### Map input: (0,0) 6 ##### Map output: (0,0,0,1) (0,0,6) ##### Map input: (0,1) 7 ##### Map output: (0,0,0,1) (0,1,7) ##### Map input: (0,2) 4 ##### Map output: (0,0,0,1) (0,2,4) ##### Map input: (1,0) 9 ##### Map output: (0,0,0,1) (1,0,9) ##### Map input: (1,1) 1 ##### Map output: (0,0,0,1) (1,1,1) ##### Map input: (1,2) 3 ##### Map output: (0,0,0,1) (1,2,3) ##### Map input: (2,0) 7 ##### Map output: (0,0,0,1) (2,0,7) ##### Map input: (2,1) 6 ##### Map output: (0,0,0,1) (2,1,6) ##### Map input: (2,2) 2 ##### Map output: (0,0,0,1) (2,2,2) </code></pre> <p>Map output for Matrix A:</p> <pre><code>##### Map setup: matrixA = true for hdfs://localhost/user/hadoop-user/A strategy = 4 R1 = 4 I = 3 K = 3 J = 3 IB = 3 KB = 3 JB = 3 ##### Map input: (1,1) 1 ##### Map output: (0,0,0,0) (1,1,1) ##### Map input: (1,2) 6 ##### Map output: (0,0,0,0) (1,2,6) ##### Map input: (2,0) 7 ##### Map output: (0,0,0,0) (2,0,7) ##### Map input: (2,1) 8 ##### Map output: (0,0,0,0) (2,1,8) ##### Map input: (2,2) 9 ##### Map output: (0,0,0,0) (2,2,9) </code></pre> <p>Notice that the Map for matrix A does not read the zeros from the input file. Note: both input files are stored in HDFS as sequence files, and the output is a sequence file too. Can someone shed some light on what the problem is? Thanks!</p> <p>The code for the Mapper class is given below:</p> <pre><code>/** The job 1 mapper class. */ private static class Job1Mapper extends Mapper&lt;IndexPair, IntWritable, Key, Value&gt; { private Path path; private boolean matrixA; private Key key = new Key(); private Value value = new Value(); public void setup (Context context) { init(context); FileSplit split = (FileSplit)context.getInputSplit(); path = split.getPath(); matrixA = path.toString().startsWith(inputPathA); if (DEBUG) { System.out.println("##### Map setup: matrixA = " + matrixA + " for " + path); System.out.println(" strategy = " + strategy); System.out.println(" R1 = " + R1); System.out.println(" I = " + I); System.out.println(" K = " + K); System.out.println(" J = " + J); System.out.println(" IB = " + IB); System.out.println(" KB = " + KB); System.out.println(" JB = " + JB); } } private void printMapInput (IndexPair indexPair, IntWritable el) { System.out.println("##### Map input: (" + indexPair.index1 + "," + indexPair.index2 + ") " + el.get()); } private void printMapOutput (Key key, Value value) { System.out.println("##### Map output: (" + key.index1 + "," + key.index2 + "," + key.index3 + "," + key.m + ") (" + value.index1 + "," + value.index2 + "," + value.v + ") "); } private void badIndex (int index, int dim, String msg) { System.err.println("Invalid " + msg + " in " + path + ": " + index + " " + dim); System.exit(1); } public void map (IndexPair indexPair, IntWritable el, Context context) throws IOException, InterruptedException { if (DEBUG) printMapInput(indexPair, el); int i = 0; int k = 0; int j = 0; if (matrixA) { i = indexPair.index1; if (i &lt; 0 || i &gt;= I) badIndex(i, I, "A row index"); k = indexPair.index2; if (k &lt; 0 || k &gt;= K) badIndex(k, K, "A column index"); } else { k = indexPair.index1; if (k &lt; 0 || k &gt;= K) badIndex(k, K, "B row index"); j = indexPair.index2; if (j &lt; 0 || j &gt;= J) badIndex(j, J, "B column index"); } value.v = el.get(); if (matrixA) { key.index1 = i/IB; key.index3 = k/KB; key.m = 0; value.index1 = i % IB; value.index2 = k % KB; for (int jb = 0; jb &lt; NJB; jb++) { key.index2 = jb; context.write(key, value); if (DEBUG) printMapOutput(key, value); } } else { key.index2 = j/JB; key.index3 = k/KB; key.m = 1; value.index1 = k % KB; value.index2 = j % JB; for (int ib = 0; ib &lt; NIB; ib++) { key.index1 = ib; context.write(key, value); if (DEBUG) printMapOutput(key, value); } } } } </code></pre> <p>If there are any syntax errors, it's only because I copy-pasted the code and modified it here, so I might have overlooked something. </p> <p>I need help with the logic of the Map function, which does not read 0's from the input file, can anyone tell me why?</p>
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    1. COThese are more than 700 lines of code. Do you think anyone will debug through this for you?
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      1. USThomas Jungblut
    2. COI modified my post to include only the mapper class code. I need help with the logic, in the sense, I am not able to come up with an explanation as to why 0's are not being read by the input file by the Map function.
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    3. CO@ThomasJungblut - I thought you would be promoting Hama for Matrix multiplication :)
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      1. USPraveen Sripati
 

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