Why is it illegal to call the mean for this 3D matrix of doublings in Scala Breeze?
I'm new to Breeze (formerly Scalala) and can't figure out why the following simple program is throwing an exception. I am using Scala 2.9.2 and Breeze 0.1:
import breeze.linalg._
val m = DenseMatrix((3.0, 1.0, 2.0), (-2.0, 1.0, 3.0))
val n = mean(m, Axis._1)
It works as expected if I use a 2x2 or 3x2 matrix, but the 2x3 matrix throws the following exception:
-- org.jblas ERROR Couldn't load copied link file: java.lang.UnsatisfiedLinkError: C:\Users\daved\AppData\Local\Temp\jblas8588491482847885553jblas.dll: Can't find dependent libraries.
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 6
at breeze.linalg.package$$anon$1.apply$mcD$sp(package.scala:203)
at breeze.linalg.package$$anon$1.apply(package.scala:196)
at breeze.linalg.package$$anon$1.apply(package.scala:186)
at breeze.linalg.DenseVector.ureduce(DenseVector.scala:91)
at breeze.linalg.Tensor$$anon$1.apply(Tensor.scala:149)
at breeze.generic.UReduceable$class.apply$mcD$sp(URFunc.scala:56)
at breeze.linalg.Tensor$$anon$1.apply$mcD$sp(Tensor.scala:148)
at breeze.generic.URFunc$mcD$sp$class.apply$mcD$sp(URFunc.scala:32)
at breeze.linalg.package$$anon$1.apply$mcD$sp(package.scala:186)
at breeze.generic.URFunc$mcD$sp$$anonfun$apply$mcD$sp$1.apply(URFunc.scala:36)
at breeze.linalg.LowPriorityDenseMatrix1$$anon$17.apply(DenseMatrix.scala:444)
at breeze.linalg.LowPriorityDenseMatrix1$$anon$17.apply(DenseMatrix.scala:440)
at breeze.generic.URFunc$mcD$sp$class.apply$mcD$sp(URFunc.scala:36)
at breeze.linalg.package$$anon$1.apply$mcD$sp(package.scala:186)
at com.tennisedge.opencv.BreezePlay$delayedInit$body.apply(BreezePlay.scala:24)
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I believe this is a bug in Breeze. In particular, implicit conversion DenseMatrix
canCollapseCols
.
If I define my own implicit conversion in a local file, then everything works as expected:
implicit def myCanCollapseCols[V, R:ClassManifest] = new CanCollapseAxis[DenseMatrix[V], Axis._1.type, DenseVector[V], R, DenseVector[R]] {
def apply(from: DenseMatrix[V], axis: Axis._1.type)(f: (DenseVector[V]) => R): DenseVector[R] = {
val result = DenseVector.zeros[R](from.rows)
val t = from.t
for(r <- 0 until t.cols) { // BUG WAS HERE: was from.cols in original defintion.
result(r) = f(t(::, r))
}
result
}
}
val m = breeze.linalg.DenseMatrix((3.0, 1.0, 2.0), (-2.0, 1.0, 3.0))
val n = breeze.linalg.mean(m, breeze.linalg.Axis._1)
This is still in my head, so I'll create a pull request for it on GitHub to fix it. In the meantime, I can just use my own implicit conversion.
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This is a perfect example (with reference to this one ) of the problem with exceptions thrown in constructors! What is disguised as a dependency problem is indeed ArrayIndexOutOfBoundsException
what was encountered in the constructor that was called on demand during class load. This is often very perplexing. (This is my "favorite" (most notorious) consequence of throwing exceptions in constructors.)
At least that's what it seems to me. I'm not really sure.
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