Question

class MatrixMultiplication {
  def singleThreadedMultiplication(m1:Seq[Array[Double]], m2:Array[Array[Double]] ) ={
    val res =  Array.fill(m1.length, m2(0).length)(0.0)

    for(row <- 0 until m1.length;
        col <- 0 until m2(0).length;
        i   <- 0 until m1(0).length){
      res(row)(col) += m1(row)(i) * m2(i)(col)
    }

    res
  }
}

__

object multiplication {
  def main(args : Seq[Array[Double]], args2 : Array[Double]) : Unit = {
    val matrixmult = new MatrixMultiplication
    var b = new Array[Double](4)
    b = Array(2,1,2,1)
    seq: Seq[Double] = WrappedArray(1, 0, 2, 0)
    matrixmult.singleThreadedMultiplication(Seq[Double],b)
  }
}

All I need is to know how I can run the single threaded multiplication method since its 1st parameter is Seq[Array[Double]] and I have no idea and I didn’t manage to find any way how to create a seq double array in the second class.

Answer 1

Seq is a trait and there are many subclasses that implement it. List and ArrayBuffer for example. So, you can create an Array[Array[Double]] and pass that to singleThreadedMultiplication. The appropriate type can be created with val array = Array(Array(1.0,2.0,3.0)) and passed to m1 or m2 in singleThreadedMultiplication for example.

object multiplication {
  def main(args : Seq[Array[Double]], args2 : Array[Double]) : Unit = {
    val matrixmult = new MatrixMultiplication
    matrixmult.singleThreadedMultiplication(args, Array(args2)
  }
}

To run it and use the parameters passed in remove these lines since they are not used.

var b = new Array[Double](4)
b = Array(2,1,2,1)
seq: Seq[Double] = WrappedArray(1, 0, 2, 0)

Then change the call to use the parameters passed in.

matrixmult.singleThreadedMultiplication(args, Array(args2))

This runs but you have an java.lang.ArrayIndexOutOfBoundsException in the singleThreadedMultiplication function.

scala> val a = Array(2.0,1.0,2.0,1.0)
b: Array[Double] = Array(2.0, 1.0, 2.0, 1.0)

scala> val b = Array(Array(1.0,0.0,2.0,0.0))
c: Array[Array[Double]] = Array(Array(1.0, 0.0, 2.0, 0.0))

scala> multiplication.main(b, a)
java.lang.ArrayIndexOutOfBoundsException: 1
at MatrixMultiplication$$anonfun$singleThreadedMultiplication$1$$anonfun$apply$mcVI$sp$1$$anonfun$apply$mcVI$sp$2.apply$mcVI$sp
...