using System;
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using System.Collections.Generic;
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using System.Drawing;
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using System.Linq;
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using System.Text;
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using System.Threading.Tasks;
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namespace ErrorAnalysis.Service
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{
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public class Utility
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{
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/// <summary>
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/// 单线性插值法
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/// </summary>
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/// <param name="value">插值</param>
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/// <param name="x0">起始值</param>
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/// <param name="y0">起始值对应值</param>
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/// <param name="x1">结束值</param>
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/// <param name="y1">结束值对应值</param>
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/// <returns>插值对应结果</returns>
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public static double Interpolate(double value, double x0, double y0, double x1, double y1)
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{
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// Calculate the interpolated value using linear interpolation formula
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double y = y0 + (value - x0) * (y1 - y0) / (x1 - x0);
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return y;
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}
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public static (double slope, double intercept) FitLine(PointF[] points)
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{
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// 计算各求和项
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int n = points.Length;
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double sumX = 0, sumY = 0, sumXY = 0, sumX2 = 0;
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foreach (var p in points)
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{
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sumX += p.X;
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sumY += p.Y;
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sumXY += p.X * p.Y;
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sumX2 += p.X * p.X;
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}
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// 计算斜率和截距
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double denominator = n * sumX2 - sumX * sumX;
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if (Math.Abs(denominator) < 1e-10) // 避免除以0
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throw new InvalidOperationException("点集过于集中，无法拟合直线");
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double slope = (n * sumXY - sumX * sumY) / denominator;
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double intercept = (sumY - slope * sumX) / n;
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return (slope, intercept);
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}
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public static double GetLineValue(double x, double slope, double intercept) => slope * x + intercept;
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public static (double a, double b, double c) FitParabola(PointF[] points)
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{
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if (points.Length < 3)
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throw new ArgumentException("至少需要3个点进行抛物线拟合");
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// 1. 计算各项求和值[1,6](@ref)
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int n = points.Length;
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double sx = 0, sy = 0, sx2 = 0, sx3 = 0, sx4 = 0, sxy = 0, sx2y = 0;
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foreach (var p in points)
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{
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double x = p.X;
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double y = p.Y;
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double x2 = x * x;
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double x3 = x2 * x;
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double x4 = x2 * x2;
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sx += x;
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sy += y;
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sx2 += x2;
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sx3 += x3;
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sx4 += x4;
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sxy += x * y;
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sx2y += x2 * y;
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}
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// 2. 构建正规方程矩阵[1,6](@ref)
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double[,] matrix = {
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{ sx4, sx3, sx2, sx2y },
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{ sx3, sx2, sx, sxy },
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{ sx2, sx, n, sy }
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};
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// 3. 使用高斯消元法求解
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double[] coefficients = GaussElimination(matrix);
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return (coefficients[0], coefficients[1], coefficients[2]);
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}
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// 高斯消元法实现（带部分主元选择）
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private static double[] GaussElimination(double[,] matrix)
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{
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int n = matrix.GetLength(0);
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double[] result = new double[n];
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// 前向消元
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for (int i = 0; i < n - 1; i++)
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{
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// 部分主元选择
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int maxRow = i;
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for (int k = i + 1; k < n; k++)
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{
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if (Math.Abs(matrix[k, i]) > Math.Abs(matrix[maxRow, i]))
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maxRow = k;
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}
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// 行交换
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if (maxRow != i)
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{
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for (int j = 0; j <= n; j++)
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{
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double temp = matrix[i, j];
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matrix[i, j] = matrix[maxRow, j];
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matrix[maxRow, j] = temp;
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}
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}
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// 消元过程
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for (int k = i + 1; k < n; k++)
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{
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double factor = matrix[k, i] / matrix[i, i];
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for (int j = i; j <= n; j++)
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{
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matrix[k, j] -= factor * matrix[i, j];
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}
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}
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}
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// 回代求解
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for (int i = n - 1; i >= 0; i--)
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{
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result[i] = matrix[i, n];
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for (int j = i + 1; j < n; j++)
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{
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result[i] -= matrix[i, j] * result[j];
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}
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result[i] /= matrix[i, i];
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}
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return result;
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}
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public static double GetParabolaValue(double x, double a, double b, double c)
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{
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return a * x * x + b * x + c;
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}
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}
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}
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