Data commit

Task/Polynomial-regression/Swift/polynomial-regression.swift

@@ -0,0 +1,41 @@
+let x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+let y = [1, 6, 17, 34, 57, 86, 121, 162, 209, 262, 321]
+
+func average(_ input: [Int]) -> Int {
+    return input.reduce(0, +) / input.count
+}
+
+func polyRegression(x: [Int], y: [Int]) {
+    let xm = average(x)
+    let ym = average(y)
+    let x2m = average(x.map { $0 * $0 })
+    let x3m = average(x.map { $0 * $0 * $0 })
+    let x4m = average(x.map { $0 * $0 * $0 * $0 })
+    let xym = average(zip(x,y).map { $0 * $1 })
+    let x2ym = average(zip(x,y).map { $0 * $0 * $1 })
+
+    let sxx = x2m - xm * xm
+    let sxy = xym - xm * ym
+    let sxx2 = x3m - xm * x2m
+    let sx2x2 = x4m - x2m * x2m
+    let sx2y = x2ym - x2m * ym
+
+    let b = (sxy * sx2x2 - sx2y * sxx2) / (sxx * sx2x2 - sxx2 * sxx2)
+    let c = (sx2y * sxx - sxy * sxx2) / (sxx * sx2x2 - sxx2 * sxx2)
+    let a = ym - b * xm - c * x2m
+
+    func abc(xx: Int) -> Int {
+        return (a + b * xx) + (c * xx * xx)
+    }
+
+    print("y = \(a) + \(b)x + \(c)x^2\n")
+    print(" Input  Approximation")
+    print(" x   y     y1")
+
+    for i in 0 ..< x.count {
+        let result = Double(abc(xx: i))
+        print(String(format: "%2d %3d  %5.1f", x[i], y[i], result))
+    }
+}
+
+polyRegression(x: x, y: y)