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Implementation taken from Flutter's LeastSquareSolver\n// https://github.com/flutter/flutter/blob/master/packages/flutter/lib/src/gestures/lsq_solver.dart\n\nclass Vector {\n private offset: number;\n private length: number;\n private elements: number[];\n\n constructor(length: number) {\n this.offset = 0;\n this.length = length;\n this.elements = new Array(length);\n }\n\n public static fromVOL(\n values: number[],\n offset: number,\n length: number\n ): Vector {\n const result = new Vector(0);\n\n result.offset = offset;\n result.length = length;\n result.elements = values;\n\n return result;\n }\n\n public get(index: number): number {\n return this.elements[this.offset + index];\n }\n\n public set(index: number, value: number): void {\n this.elements[this.offset + index] = value;\n }\n\n public dot(other: Vector): number {\n let result = 0;\n for (let i = 0; i < this.length; i++) {\n result += this.get(i) * other.get(i);\n }\n return result;\n }\n\n public norm() {\n return Math.sqrt(this.dot(this));\n }\n}\n\nclass Matrix {\n private columns: number;\n private elements: number[];\n\n constructor(rows: number, columns: number) {\n this.columns = columns;\n this.elements = new Array(rows * columns);\n }\n\n public get(row: number, column: number): number {\n return this.elements[row * this.columns + column];\n }\n\n public set(row: number, column: number, value: number): void {\n this.elements[row * this.columns + column] = value;\n }\n\n public getRow(row: number): Vector {\n return Vector.fromVOL(this.elements, row * this.columns, this.columns);\n }\n}\n\n/// An nth degree polynomial fit to a dataset.\nclass PolynomialFit {\n /// The polynomial coefficients of the fit.\n ///\n /// For each `i`, the element `coefficients[i]` is the coefficient of\n /// the `i`-th power of the variable.\n public coefficients: number[];\n\n /// Creates a polynomial fit of the given degree.\n ///\n /// There are n + 1 coefficients in a fit of degree n.\n constructor(degree: number) {\n this.coefficients = new Array(degree + 1);\n }\n}\n\nconst precisionErrorTolerance = 1e-10;\n\n/// Uses the least-squares algorithm to fit a polynomial to a set of data.\nexport default class LeastSquareSolver {\n /// The x-coordinates of each data point.\n private x: number[];\n /// The y-coordinates of each data point.\n private y: number[];\n /// The weight to use for each data point.\n private w: number[];\n\n /// Creates a least-squares solver.\n ///\n /// The [x], [y], and [w] arguments must not be null.\n constructor(x: number[], y: number[], w: number[]) {\n this.x = x;\n this.y = y;\n this.w = w;\n }\n\n /// Fits a polynomial of the given degree to the data points.\n ///\n /// When there is not enough data to fit a curve null is returned.\n public solve(degree: number): PolynomialFit | null {\n if (degree > this.x.length) {\n // Not enough data to fit a curve.\n return null;\n }\n\n const result = new PolynomialFit(degree);\n\n // Shorthands for the purpose of notation equivalence to original C++ code.\n const m = this.x.length;\n const n = degree + 1;\n\n // Expand the X vector to a matrix A, pre-multiplied by the weights.\n const a = new Matrix(n, m);\n for (let h = 0; h < m; h++) {\n a.set(0, h, this.w[h]);\n\n for (let i = 1; i < n; i++) {\n a.set(i, h, a.get(i - 1, h) * this.x[h]);\n }\n }\n\n // Apply the Gram-Schmidt process to A to obtain its QR decomposition.\n\n // Orthonormal basis, column-major ordVectorer.\n const q = new Matrix(n, m);\n // Upper triangular matrix, row-major order.\n const r = new Matrix(n, m);\n\n for (let j = 0; j < n; j += 1) {\n for (let h = 0; h < m; h += 1) {\n q.set(j, h, a.get(j, h));\n }\n for (let i = 0; i < j; i += 1) {\n const dot = q.getRow(j).dot(q.getRow(i));\n for (let h = 0; h < m; h += 1) {\n q.set(j, h, q.get(j, h) - dot * q.get(i, h));\n }\n }\n\n const norm = q.getRow(j).norm();\n if (norm < precisionErrorTolerance) {\n // Vectors are linearly dependent or zero so no solution.\n return null;\n }\n\n const inverseNorm = 1.0 / norm;\n for (let h = 0; h < m; h += 1) {\n q.set(j, h, q.get(j, h) * inverseNorm);\n }\n for (let i = 0; i < n; i += 1) {\n r.set(j, i, i < j ? 0.0 : q.getRow(j).dot(a.getRow(i)));\n }\n }\n\n // Solve R B = Qt W Y to find B. This is easy because R is upper triangular.\n // We just work from bottom-right to top-left calculating B's coefficients.\n const wy = new Vector(m);\n for (let h = 0; h < m; h += 1) {\n wy.set(h, this.y[h] * this.w[h]);\n }\n for (let i = n - 1; i >= 0; i -= 1) {\n result.coefficients[i] = q.getRow(i).dot(wy);\n for (let j = n - 1; j > i; j -= 1) {\n result.coefficients[i] -= r.get(i, j) * result.coefficients[j];\n }\n result.coefficients[i] /= r.get(i, i);\n }\n\n return result;\n }\n}\n"]}