用.NET语言写一个计算股票技术指标DMI的函数，第一个参数为datatable类型，另外两个参数为int型；日期列名为“日期”，开盘价列名为“开盘”,收盘价列名为“收盘”,最高价列名为“最高”,最低价列名为“最低”，返回值为datatable类型，返回值包含PDI,MDI,ADX,ADXR等列，double类型全部四舍五入保留3位小数。

好的，以下是用.NET语言写的计算DMI指标的函数：

public static DataTable CalculateDMI(DataTable table, int n, int m)
{
    // 计算TR、+DI、-DI、DX
    double[] tr = new double[table.Rows.Count];
    double[] pdm = new double[table.Rows.Count];
    double[] mdm = new double[table.Rows.Count];
    double[] pdi = new double[table.Rows.Count];
    double[] mdi = new double[table.Rows.Count];
    double[] dx = new double[table.Rows.Count];

    for (int i = 1; i < table.Rows.Count; i++)
    {
        double h1 = Convert.ToDouble(table.Rows[i]["最高"]);
        double l1 = Convert.ToDouble(table.Rows[i]["最低"]);
        double c1 = Convert.ToDouble(table.Rows[i]["收盘"]);
        double h2 = Convert.ToDouble(table.Rows[i - 1]["最高"]);
        double l2 = Convert.ToDouble(table.Rows[i - 1]["最低"]);
        double c2 = Convert.ToDouble(table.Rows[i - 1]["收盘"]);

        tr[i] = Math.Max(Math.Max(h1 - l1, Math.Abs(h1 - c2)), Math.Abs(l1 - c2));

        pdm[i] = Math.Max(h1 - h2, 0);
        mdm[i] = Math.Max(l2 - l1, 0);

        if (pdm[i] > mdm[i])
        {
            pdm[i] -= mdm[i];
            mdm[i] = 0;
        }
        else
        {
            mdm[i] -= pdm[i];
            pdm[i] = 0;
        }
    }

    for (int i = n; i < table.Rows.Count; i++)
    {
        double sum_tr = 0;
        double sum_pdm = 0;
        double sum_mdm = 0;

        for (int j = i - n + 1; j <= i; j++)
        {
            sum_tr += tr[j];
            sum_pdm += pdm[j];
            sum_mdm += mdm[j];
        }

        pdi[i] = 100 * sum_pdm / sum_tr;
        mdi[i] = 100 * sum_mdm / sum_tr;

        if (pdi[i] + mdi[i] == 0)
        {
            dx[i] = 0;
        }
        else
        {
            dx[i] = 100 * Math.Abs(pdi[i] - mdi[i]) / (pdi[i] + mdi[i]);
        }
    }

    // 计算ADX、ADXR
    double[] adx = new double[table.Rows.Count];
    double[] adxr = new double[table.Rows.Count];

    for (int i = m; i < table.Rows.Count; i++)
    {
        double sum_dx = 0;
        for (int j = i - m + 1; j <= i; j++)
        {
            sum_dx += dx[j];
        }
        adx[i] = sum_dx / m;

        adxr[i] = (adx[i] + adx[i - m]) / 2;
    }

    // 返回结果
    DataTable result = new DataTable();
    result.Columns.Add("日期", typeof(DateTime));
    result.Columns.Add("PDI", typeof(double));
    result.Columns.Add("MDI", typeof(double));
    result.Columns.Add("ADX", typeof(double));
    result.Columns.Add("ADXR", typeof(double));

    for (int i = m; i < table.Rows.Count; i++)
    {
        DataRow row = result.NewRow();
        row["日期"] = table.Rows[i]["日期"];
        row["PDI"] = Math.Round(pdi[i], 3);
        row["MDI"] = Math.Round(mdi[i], 3);
        row["ADX"] = Math.Round(adx[i], 3);
        row["ADXR"] = Math.Round(adxr[i], 3);
        result.Rows.Add(row);
    }

    return result;
}

其中，n和m分别为计算DMI指标的参数，table为输入的股票数据表，返回值为包含PDI、MDI、ADX、ADXR等列的数据表。函数内部首先计算TR、+DI、-DI、DX等指标，然后根据这些指标计算ADX和ADXR，并将结果保存在结果数据表中。注意，函数内部的所有double类型都使用了四舍五入保留3位小数。