Paul Hubenig created MAHOUT-1078:
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Summary: matrixmult gives wrong answer
Key: MAHOUT-1078
URL: https://issues.apache.org/jira/browse/MAHOUT-1078
Project: Mahout
Issue Type: Bug
Components: Math
Affects Versions: 0.7
Reporter: Paul Hubenig
Create a simple matrix:
1 2
3 4
package exp
import org.apache.hadoop.conf.Configuration
import org.apache.hadoop.fs.Path
import org.apache.hadoop.io.{IOUtils, IntWritable, SequenceFile}
import org.apache.mahout.math.{SequentialAccessSparseVector, VectorWritable,
RandomAccessSparseVector}
object MakeMatrix extends App with CommonMethods {
val matrixFileOutput = "/Users/phubenig/matrixFile.sf"
val conf = new Configuration()
val fs = getFileSystem(true, conf)
val path = new Path(matrixFileOutput)
val arr = Array(Array(1, 2), Array(3, 4))
val rank = 2
val key = new org.apache.hadoop.io.IntWritable()
val writer = SequenceFile.createWriter(fs, conf, path, classOf[IntWritable],
classOf[VectorWritable])
for (i <- 0 until rank) {
key.set(i)
val v = new SequentialAccessSparseVector(rank)
for (j <- 0 until rank) {
v.setQuick(j, arr(i)(j))
}
writer.append(key, new VectorWritable(v))
}
IOUtils.closeStream(writer)
}
Engage mahout to square this matrix.
$ mahout matrixmult --numRowsA 2 --numColsA 2 --numRowsB 2 --numColsB 2
--inputPathA matrixFile.sf --inputPathB matrixFile.sf
Read back the result:
I get the answer:??
(0, 0): 10.0
(0, 1): 14.0
(1, 0): 14.0
(1, 1): 20.0
i.e.,
10 14
14 20
Correct answer??
1 2 1 2 7 10
x =
3 4 3 4 15 22
I tried mahout transpose and that seems to work.
Am I specifying the matrix wrong somehow?
10 =|(1, 3)| * |(1,3)|
20 =|(2,4)| * |(2,4)|
14 = (1,3) , (2,4)
but why is it doing this?
Instead of two vectors in the matrix creation program, I also tried one vector
consisting of: (1, 2, 3, 4) - matrixmult also give the wrong answer.
Regardless of convention used (???) that I don't understand, here is no
documentation and no error checking.
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