June 2018 Update

Task/Polynomial-regression/Kotlin/polynomial-regression.kotlin

@@ -0,0 +1,38 @@
+// version 1.1.51
+
+fun polyRegression(x: IntArray, y: IntArray) {
+    val n = x.size
+    val r = 0 until n
+    val xm = x.average()
+    val ym = y.average()
+    val x2m = r.map { it * it }.average()
+    val x3m = r.map { it * it * it }.average()
+    val x4m = r.map { it * it * it * it }.average()
+    val xym = x.zip(y).map { it.first * it.second }.average()
+    val x2ym = x.zip(y).map { it.first * it.first * it.second }.average()
+
+    val sxx = x2m - xm * xm
+    val sxy = xym - xm * ym
+    val sxx2 = x3m - xm * x2m
+    val sx2x2 = x4m - x2m * x2m
+    val sx2y = x2ym - x2m * ym
+
+    val b = (sxy * sx2x2 - sx2y * sxx2) / (sxx * sx2x2 - sxx2 * sxx2)
+    val c = (sx2y * sxx - sxy * sxx2) / (sxx * sx2x2 - sxx2 * sxx2)
+    val a = ym - b * xm - c * x2m
+
+    fun abc(xx: Int) = a + b * xx + c * xx * xx
+
+    println("y = $a + ${b}x + ${c}x^2\n")
+    println(" Input  Approximation")
+    println(" x   y     y1")
+    for (i in 0 until n) {
+        System.out.printf("%2d %3d  %5.1f\n", x[i], y[i], abc(x[i]))
+    }
+}
+
+fun main(args: Array<String>) {
+    val x = IntArray(11) { it }
+    val y = intArrayOf(1, 6, 17, 34, 57, 86, 121, 162, 209, 262, 321)
+    polyRegression(x, y)
+}