scala source code of LocalMinPlus

import org.apache.spark.mllib.linalg.distributed.{CoordinateMatrix, MatrixEntry}
import org.scalatest.{FlatSpec}
import breeze.linalg.{DenseMatrix => BDM, DenseVector, min, Matrix =>BM}
import AllPairsShortestPath._

/**
 * Created by arzav on 5/26/15.
 */
class LocalMinPlus extends FlatSpec {

  def localMinPlus(A: BDM[Double], B: BDM[Double]): BDM[Double] = {
    require(A.cols == B.rows, " Num cols of A does not match the num rows of B")
    val k = A.cols
    val onesA = DenseVector.ones[Double](B.cols)
    val onesB = DenseVector.ones[Double](A.rows)
    var AMinPlusB = A(::, 0) * onesA.t + onesB * B(0, ::)
    if (k > 1) {
      for (i <- 1 until k) {
        val a = A(::, i)
        val b = B(i, ::)
        val aPlusb = a * onesA.t + onesB * b
        AMinPlusB = min(aPlusb, AMinPlusB)
      }
    }
    AMinPlusB
  }


  def fourByFourBlockMatrx = {
    BDM(
      (0.0, 20.0, 4.0, 2.0),
      (2.0, 0.0, 1.0, 3.0),
      (1.0, 6.0, 0.0, 5.0),
      (4.0, 2.0, 2.0, 0.0)
    )
  }

  def fourByFourMinPlusProduct = {
    BDM(
      (0.0,  2.0,  1.0,  2.0),
      (2.0,  0.0,  1.0,  2.0),
      (1.0,  1.0,  0.0,  2.0),
      (2.0,  2.0,  2.0,  0.0)
    )
  }

  "The minPlus product of the sample 4x4 matrix with itself" should "be correct" in {
    assert(localMinPlus(fourByFourBlockMatrx, fourByFourBlockMatrx.t) === fourByFourMinPlusProduct)
  }
}