September 2017 Update

Task/Matrix-exponentiation-operator/Kotlin/matrix-exponentiation-operator.kotlin

@@ -0,0 +1,57 @@
+// version 1.1.3
+
+typealias Vector = DoubleArray
+typealias Matrix = Array<Vector>
+
+operator fun Matrix.times(other: Matrix): Matrix {
+    val rows1 = this.size
+    val cols1 = this[0].size
+    val rows2 = other.size
+    val cols2 = other[0].size
+    require(cols1 == rows2)
+    val result = Matrix(rows1) { Vector(cols2) }
+    for (i in 0 until rows1) {
+        for (j in 0 until cols2) {
+            for (k in 0 until rows2) {
+                result[i][j] += this[i][k] * other[k][j]
+            }
+        }
+    }
+    return result
+}
+
+fun identityMatrix(n: Int): Matrix {
+    require(n >= 1)
+    val ident = Matrix(n) { Vector(n) }
+    for (i in 0 until n) ident[i][i] = 1.0
+    return ident
+}
+
+infix fun Matrix.pow(n : Int): Matrix {
+    require (n >= 0 && this.size == this[0].size)
+    if (n == 0) return identityMatrix(this.size)
+    if (n == 1) return this
+    var pow = identityMatrix(this.size)
+    var base = this
+    var e = n
+    while (e > 0) {
+        if ((e and 1) == 1) pow *= base
+        e = e shr 1
+        base *= base
+    }
+    return pow
+}
+
+fun printMatrix(m: Matrix, n: Int) {
+    println("** Power of $n **")
+    for (i in 0 until m.size) println(m[i].contentToString())
+    println()
+}
+
+fun main(args: Array<String>) {
+    val m = arrayOf(
+        doubleArrayOf(3.0, 2.0),
+        doubleArrayOf(2.0, 1.0)
+    )
+    for (i in 0..10) printMatrix(m pow i, i)
+}