using System;

​

public class Program

{

    public static void Main(string[] args)

    {

        double[] xVal = new double[]{0, 1, 2};

        double[] yVal = new double[]{20, 22, 24};

        double rsquared;

        double yintercept;

        double slope;

        LinearRegression(xVal, yVal, 0, xVal.Length, out rsquared, out yintercept, out slope);

        Console.WriteLine("offset: " + yintercept);

        Console.WriteLine("gain: " + slope);

        Console.WriteLine(yintercept + (slope * 15)); //15 is xvalue of future(no of day from 1)

    }

​

    public static void LinearRegression(double[] xVals, double[] yVals, int inclusiveStart, int exclusiveEnd, out double rsquared, out double yintercept, out double slope)

    {

        //Debug.Assert(xVals.Length == yVals.Length);

        double sumOfX = 0;

        double sumOfY = 0;

        double sumOfXSq = 0;

        double sumOfYSq = 0;

        double ssX = 0;

        double ssY = 0;

        double sumCodeviates = 0;

        double sCo = 0;

        double count = exclusiveEnd - inclusiveStart;

        for (int ctr = inclusiveStart; ctr < exclusiveEnd; ctr++)

        {

            double x = xVals[ctr];

            double y = yVals[ctr];

            sumCodeviates += x * y;

            sumOfX += x;

            sumOfY += y;

            sumOfXSq += x * x;

            sumOfYSq += y * y;

        }

​

        ssX = sumOfXSq - ((sumOfX * sumOfX) / count);

        ssY = sumOfYSq - ((sumOfY * sumOfY) / count);

        double RNumerator = (count * sumCodeviates) - (sumOfX * sumOfY);

        double RDenom = (count * sumOfXSq - (sumOfX * sumOfX)) * (count * sumOfYSq - (sumOfY * sumOfY));

        sCo = sumCodeviates - ((sumOfX * sumOfY) / count);

        double meanX = sumOfX / count;

        double meanY = sumOfY / count;

        double dblR = RNumerator / Math.Sqrt(RDenom);

        rsquared = dblR * dblR;

        yintercept = meanY - ((sCo / ssX) * meanX);

        slope = sCo / ssX;

    }

}