DenseMatrix[Int] multiplication problem

[Sungho Ham]

Hi.

Multiplication of DenseMatrix.eye[Int] gives zero when matrix size over 2000.

I tested with two BLAS, but they gave same wrong result.

build.sbt

scalaVersion := "2.11.11"

"org.scalanlp" %% "breeze" % "0.13.2"

"org.scalanlp" %% "breeze-natives" % "0.12"

test function

def mulTest(size: Int): Unit = {

val b = BLAS.getInstance()

println(s"BLAS = $b")

val simMatrix1 = DenseMatrix.eye[Int](size)

println((simMatrix1 * simMatrix1).valueAt(0, 0))

}

1. NativeBLAS

----- code -----

mulTest(2000)

mulTest(2001)

----- result -----

BLAS = com.github.fommil.netlib.NativeSystemBLAS@72b6cbcc

1

BLAS = com.github.fommil.netlib.NativeSystemBLAS@72b6cbcc

0

2. F2jBlas

----- VM options ----- 

-Dcom.github.fommil.netlib.BLAS=com.github.fommil.netlib.F2jBLAS

-Dcom.github.fommil.netlib.LAPACK=com.github.fommil.netlib.F2jLAPACK

-Dcom.github.fommil.netlib.ARPACK=com.github.fommil.netlib.F2jARPACK

----- code -----

mulTest(2000)

mulTest(2001)

----- result -----

BLAS = com.github.fommil.netlib.F2jBLAS@4f970963

1

BLAS = com.github.fommil.netlib.F2jBLAS@4f970963

0

Thanks.

[David Hall]

Oof.

I have a hand-rolled matrix multiply for ints since it's not in blas, and 2000 is a blocksize threshold. sorry about that. I'll fix it

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[David Hall]

(fixed in master)

[Sungho Ham]

Thank for your help, David!

I will use Double instead of Int for a while.

2018년 1월 17일 수요일 오후 12시 56분 17초 UTC+9, David Hall 님의 말:

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[David Hall]

Honestly, assuming you're using native blas and not f2j (and you're not worrying about integer overflow/underflow), doubles are always going to be faster. I almost just made Int/Int matrix multiply just convert everything to doubles, but i decided not to.

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[Sungho Ham]

I agree with your decision. Implicit convert to double will cause unexpected result for user.

Thank you again for your support. 

2018년 1월 17일 수요일 오후 2시 6분 22초 UTC+9, David Hall 님의 말: