用.NET语言写出计算股票技术指标KDJ，4个参数，第一个参数为datatable类型，其他为int型，返回值为datatable类型，double类型全部四舍五入保留3位小数。

非常感谢您的问题！以下是用.NET语言编写计算股票技术指标KDJ的代码：

public static DataTable CalculateKDJ(DataTable dataTable, int n, int m1, int m2)
{
    DataTable resultTable = new DataTable();
    resultTable.Columns.Add("K", typeof(double));
    resultTable.Columns.Add("D", typeof(double));
    resultTable.Columns.Add("J", typeof(double));

    double[] high = new double[dataTable.Rows.Count];
    double[] low = new double[dataTable.Rows.Count];
    double[] close = new double[dataTable.Rows.Count];
    double[] rsv = new double[dataTable.Rows.Count];
    double[] k = new double[dataTable.Rows.Count];
    double[] d = new double[dataTable.Rows.Count];
    double[] j = new double[dataTable.Rows.Count];

    for (int i = 0; i < dataTable.Rows.Count; i++)
    {
        high[i] = Convert.ToDouble(dataTable.Rows[i]["High"]);
        low[i] = Convert.ToDouble(dataTable.Rows[i]["Low"]);
        close[i] = Convert.ToDouble(dataTable.Rows[i]["Close"]);

        double maxHigh = high.Skip(Math.Max(0, i - n + 1)).Take(n).Max();
        double minLow = low.Skip(Math.Max(0, i - n + 1)).Take(n).Min();

        rsv[i] = (close[i] - minLow) / (maxHigh - minLow) * 100;

        if (i == 0)
        {
            k[i] = 50;
            d[i] = 50;
        }
        else
        {
            k[i] = (m1 - 1) * k[i - 1] / m1 + rsv[i] / m1;
            d[i] = (m2 - 1) * d[i - 1] / m2 + k[i] / m2;
        }

        j[i] = 3 * k[i] - 2 * d[i];

        DataRow newRow = resultTable.NewRow();
        newRow["K"] = Math.Round(k[i], 3);
        newRow["D"] = Math.Round(d[i], 3);
        newRow["J"] = Math.Round(j[i], 3);
        resultTable.Rows.Add(newRow);
    }

    return resultTable;
}

其中，参数n表示KDJ指标的周期，m1和m2分别表示平滑系数，dataTable是包含股票数据的DataTable对象。函数返回一个包含KDJ指标计算结果的DataTable对象，其中K、D、J分别表示KDJ指标的三条线。

希望这个代码能够帮到您！