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