How to apply a user defined function to the breeze matrix elementwise

[Alexander Ulanov]

Dear Breeze developers,

I need to apply user-defined function to the breeze matrix or vector in element-wise manner. Functions can have 1,2 and 3 arguments: 

e.g. Double => Double, (Double, Double) => Double and (Double, Double, Double) => Double. 

I need also to provide the matrix that should be used to store the result of function application breeze.linalg.DenseMatrix[Double]. Can I use UFunc with InPlaceImpl? If yes, could you give me an example?

Best regards, Alexander

[David Hall]

to be clear, you presumably want something that takes 1, 2 and 3 identically structured matrices?

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[Alexander Ulanov]

Yes

[David Hall]

ok, well, there's .map on DenseMatrix, of course, but 2-ary and 3-ary there's nothing atm. I'll see about making something nowish

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[David Hall]

Already, pushed a change to allow easy UFuncification for binary and unary ufuncs:

test("WrappedUFunc") {
  val f = UFunc(math.exp _)
  assert(f(3.0) == math.exp(3.0))
  assert(f(DenseVector(3.0)) == DenseVector(math.exp(3.0)))
  assert(f(DenseMatrix(3.0)) == DenseMatrix(math.exp(3.0)))
}

test("WrappedUFunc2") {
  val f = UFunc(math.pow _)
  assert(f(3.0, 4.0) == math.pow(3.0, 4.0))
  assert(f(DenseVector(3.0), 4.0) == DenseVector(math.pow(3.0, 4.0)))
  assert(f(DenseMatrix(3.0), DenseMatrix(4.0)) == DenseMatrix(math.pow(3.0, 4.0)))
}

[David Hall]

already -> alright

[Alexander Ulanov]

Thank you! Does that allow specifying the output DenseMatrix? I.e. there is matrix X, I want to apply function Double => Double and put the result in the matrix Y?

[David Hall]

CanMapValues and CanZipMapValues are the type classes to use

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[Alexander Ulanov]

Could you give an example? If I want to compute exponent of x and put the result to y?

var x: BDV[Double]

var y: BDV[Double]

val f = UFunc(math.exp _)

....?

[David Hall]

ah, I misunderstood. Breeze has basically no support right now for specifying "sinks" for an operation. It's something I want to add, but I haven't gotten there yet.

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