I’m building a .net page to mimic a spreadsheet. The sheet contains this formula

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Asked: May 25, 20262026-05-25T16:42:32+00:00 2026-05-25T16:42:32+00:00

I’m building a .net page to mimic a spreadsheet. The sheet contains this formula

0

I’m building a .net page to mimic a spreadsheet. The sheet contains this formula

=ROUND(TREND(AA7:AE7,AA$4:AE$4,AF$4),1)

Can someone provide the C# equivalent of TREND() ? Alternatively if anyone can provide a shortcut around it that’s fine too; I’m not familiar enough with the math there to know if there’s an easier way.

Here are some sample numbers if it helps.

AA7:AE7
6 8 10 12 14

or
10.2 13.6 17.5 20.4 23.8

AA$4:AE$4
600 800 1000 1200 1400

AF$4
650

edit: here’s what I came up with and it seems to be producing the same numbers as my spreadsheet.

public static partial class Math2
{
    public static double[] Trend(double[] known_y, double[] known_x, params double[] new_x)
    {
        // return array of new y values
        double m, b;
        Math2.LeastSquaresFitLinear(known_y, known_x, out m, out b);

        List<double> new_y = new List<double>();
        for (int j = 0; j < new_x.Length; j++)
        {
            double y = (m * new_x[j]) + b;
            new_y.Add(y);
        }

        return new_y.ToArray();
    }

    // found at http://stackoverflow.com/questions/7437660/how-do-i-recreate-an-excel-formula-which-calls-trend-in-c
    // with a few modifications
    public static void LeastSquaresFitLinear(double[] known_y, double[] known_x, out double M, out double B)
    {
        if (known_y.Length != known_x.Length)
        {
            throw new ArgumentException("arrays are unequal lengths");
        }

        int numPoints = known_y.Length;

        //Gives best fit of data to line Y = MC + B
        double x1, y1, xy, x2, J;

        x1 = y1 = xy = x2 = 0.0;
        for (int i = 0; i < numPoints; i++)
        {
            x1 = x1 + known_x[i];
            y1 = y1 + known_y[i];
            xy = xy + known_x[i] * known_y[i];
            x2 = x2 + known_x[i] * known_x[i];
        }

        M = B = 0;
        J = ((double)numPoints * x2) - (x1 * x1);

        if (J != 0.0)
        {
            M = (((double)numPoints * xy) - (x1 * y1)) / J;
            //M = Math.Floor(1.0E3 * M + 0.5) / 1.0E3; // TODO this is disabled as it seems to product results different than excel
            B = ((y1 * x2) - (x1 * xy)) / J;
            // B = Math.Floor(1.0E3 * B + 0.5) / 1.0E3; // TODO assuming this is the same as above
        }
    }

}