linear equation solver from array of "DataPoints" a protocol that expects (x:Number, y:Number) tuple

linear_solver.swift

    //https://developer.apple.com/documentation/accelerate/working_with_matrices
    // e.g. https://www.youtube.com/watch?v=wBxUa9tHkkE&list=PLMiyQ6EW11_lJT2YKm7kz_Uaa7M0LbBkP

typealias Number = Double

static func solveLinearPair(cx1:Number, cy1:Number, s1:Number, cx2:Number, cy2:Number, s2:Number) -> SIMD2<Number> {
    let a = simd_double2x2(rows: [
        simd_double2(cx1, cy1),
        simd_double2(cx2, cy2)
    ])
    let b = simd_double2(s1, s2)
    return simd_mul(a.inverse, b)
}

public extension Array where Element == DataPoint {

  func unzipDataPoints() -> (inputs:[Number], outputs:[Number])  {
    var inputs = [Number]()
    var results = [Number]()
    
    inputs.reserveCapacity(count)
    results.reserveCapacity(count)
    
    forEach { dp in
        inputs.append(dp.x)
        results.append(dp.y)
    }
    
    return (inputs, results)
}

func findLine() -> (m:Number, b:Number) {
    let splitData = self.unzipDataPoints()
    
    let cx1_SigmaXk2:Number = splitData.inputs.sumOfSquares()  //vDSP.sumOfSquares
    let cy1_SigmaXk:Number = splitData.inputs.reduce(0, +)
    let cx2_SigmaXk:Number = splitData.inputs.reduce(0, +)
    let cy2_n:Number = Double(self.count) as Number
    
    let xkyk = vDSP.multiply(splitData.inputs, splitData.outputs)
    
    let s1_SigmaXkYk:Number = xkyk.reduce(0, +)
    let s2_SigmaYk:Number = splitData.outputs.reduce(0, +)
    
    let result = solveLinearPair(cx1: cx1_SigmaXk2, cy1: cy1_SigmaXk, s1: s1_SigmaXkYk, cx2: cx2_SigmaXk, cy2: cy2_n, s2: s2_SigmaYk)
    
    return (result.x, result.y)
}
}