「プログラマの為の数学勉強会」の資料を ScalaNLP で写経してみたかった http://nineties.github.io/math-seminar/

part7.scala

import breeze.linalg._

/*
 * p.15 (http://nineties.github.io/math-seminar/7.html#/15)
 * 
 * Note: Does breeze basically recommend side effects?
 * Note: The compiler will complain 'could not find implicit value for parameter canMapValues'
 *       if you make the type parameter 'Int' as a generic type.
 */
def matAdd(a: DenseMatrix[Int], b: DenseMatrix[Int]) =
  if ((a.rows, a.cols) == (b.rows, b.cols)) {
    a.mapPairs((ka, va) => va + b(ka))
  } else {
    throw new IllegalArgumentException
  }

def matScale(a: DenseMatrix[Int], k: Int) = a.map(_ * k)

def matMul(a: DenseMatrix[Int], b: DenseMatrix[Int]) =
  if (a.cols == b.rows) {
    val c = DenseMatrix.zeros[Int](a.rows, b.cols)
    (0 until a.rows).foreach { i =>
      (0 until b.cols).foreach { j =>
        var v = 0
        (0 until a.cols).foreach { k =>
          v += a(i, k) * b(k, j)
        }
        c(i, j) = v
      }
    }
    c
  } else {
    throw new IllegalArgumentException
  }

val a = DenseMatrix((1, 2, 3), (4, 5, 6))
val b = DenseMatrix((2, 1, 4), (5, 2, 1))

matAdd(a, b) == a + b
matScale(a, 2) == a * 2

val a = DenseMatrix((1, 2, 3), (4, 5, 6))
val b = DenseMatrix((2, 1, 4), (5, 2, 1), (0, 1, 3))

matMul(a, b) == a * b

/*
 * p.43 (http://nineties.github.io/math-seminar/7.html#/43)
 */
def fib(n: Int) = Iterator.fill(n)(DenseMatrix((1L, 1L), (1L, 0L))).reduceLeft(_ * _)(1, 0)

setup.sh

git clone https://github.com/scalanlp/breeze-examples
sbt console