Implement elementwise UFunc in Scala Breeze

Question

I'm trying to implement my own elementwise UFunc for a Scala Breeze matrix, so that the function can be applied to each element of a matrix. Using the Breeze.numerics package as a guide I have tried:

object step extends UFunc with MappingUFunc {
implicit object stepImplDouble extends Impl[Double, Double] {
  def apply(x: Double) = if (x >= 0.5) 1.0 else 0.0
}

Looks pretty easy, huh? I am trying to use the function as follows:

val H: BDM[Double] = step((M(::,*) + bias).t)

i.e. apply it a function element by element, to a matrix, giving an output H. However the code gives an error at compile time:

Error:(60, 26) could not find implicit value for parameter impl: dev.elm.step.Impl[breeze.linalg.DenseMatrix[Double],VR]
  case "step" => step((M(::, *) + bias).t)
Error:(60, 26) not enough arguments for method apply: (implicit impl: dev.elm.step.Impl[breeze.linalg.DenseMatrix[Double],VR])VR in trait UFunc.
Unspecified value parameter impl.
  case "step" => step((M(::, *) + bias).t)

This is very similar to the error I raised in my previous question. It sounds like it might need the matrix arguments but I thought that was all dealt with in the MappingUFunc trait. Any help appreciated! Thanks

Answer 1

Because this is an object, the declaration order matters. Either place it higher in the code than the first call, or pull it out into its own file.