             .reduce(0, +)
     }
     
-    /// Sum of the product of x and y
+    /**
+     Sum of the product of x and y
+     */
     private func sumXY(data: [[Double]]) -> Double {
         return data
             .map({

            square(v: sum[v]!() / Double(count))
    }
    
    /// The intercept
    /// a = (ΣY - b(ΣX)) / N
    private func aIntercept(b: Double) -> Double {
        return (sum(vector: yVector) / Double(count)) -
            (b * (sum(vector: xVector) / Double(count)))
    }
    
    /// The slope, or the regression coefficient
    /// b = ((ΣXY / N) - (ΣX / N)(ΣY / N)) / (Σv² / N) - (Σv / N)²
    private func bSlope() -> Double {
        return ((sumXY(data: data) / Double(count)) -
            ((sum(vector: xVector) / Double(count)) *

        let y = round_(number: model(x))
        
        return Result(
            lnModel: "\(a) + \(b)x",
            cor: round_(number: corCoefficient(b: b)),
            x: x,
            y: y
