用.NET语言写出计算股票技术指标DMI的函数，第一个参数为datatable类型，其他参数为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。所有double类型保留3位小数。

好的，我会用.NET语言写出计算股票技术指标DMI的函数，以下是代码：

public static DataTable CalculateDMI(DataTable dt, int n, int m)
{
    DataTable resultDt = new DataTable();
    resultDt.Columns.Add("日期", typeof(string));
    resultDt.Columns.Add("PDI", typeof(double));
    resultDt.Columns.Add("MDI", typeof(double));
    resultDt.Columns.Add("ADX", typeof(double));
    resultDt.Columns.Add("ADXR", typeof(double));

    // 计算TR、HD和LD
    double[] trArr = new double[dt.Rows.Count];
    double[] hdArr = new double[dt.Rows.Count];
    double[] ldArr = new double[dt.Rows.Count];
    for (int i = 0; i < dt.Rows.Count; i++)
    {
        double h = Convert.ToDouble(dt.Rows[i]["最高"]);
        double l = Convert.ToDouble(dt.Rows[i]["最低"]);
        double pc = i > 0 ? Convert.ToDouble(dt.Rows[i - 1]["收盘"]) : 0;
        double tr = Math.Max(h - l, Math.Max(Math.Abs(h - pc), Math.Abs(l - pc)));
        double hd = h - pc;
        double ld = pc - l;
        trArr[i] = tr;
        hdArr[i] = hd;
        ldArr[i] = ld;
    }

    // 计算PDI、MDI、ADX和ADXR
    double[] pdiArr = new double[dt.Rows.Count];
    double[] mdiArr = new double[dt.Rows.Count];
    double[] dxArr = new double[dt.Rows.Count];
    double[] adxArr = new double[dt.Rows.Count];
    double[] adxrArr = new double[dt.Rows.Count];
    double pdi = 0;
    double mdi = 0;
    double dx = 0;
    double adx = 0;
    double sumPdi = 0;
    double sumMdi = 0;
    double sumDx = 0;
    double sumAdx = 0;
    for (int i = 0; i < dt.Rows.Count; i++)
    {
        if (i < n)
        {
            pdiArr[i] = 0;
            mdiArr[i] = 0;
            dxArr[i] = 0;
            adxArr[i] = 0;
            adxrArr[i] = 0;
            continue;
        }
        if (i == n)
        {
            sumPdi = pdiArr.Take(n).Sum();
            sumMdi = mdiArr.Take(n).Sum();
            sumDx = dxArr.Take(n).Sum();
            sumAdx = adxArr.Take(n).Sum();
        }
        else
        {
            sumPdi = sumPdi - pdiArr[i - n - 1] + pdiArr[i - 1];
            sumMdi = sumMdi - mdiArr[i - n - 1] + mdiArr[i - 1];
            sumDx = sumDx - dxArr[i - n - 1] + dxArr[i - 1];
            sumAdx = sumAdx - adxArr[i - n - 1] + adxArr[i - 1];
        }
        double trSum = trArr.Skip(i - n).Take(n).Sum();
        double hdSum = hdArr.Skip(i - n).Take(n).Sum();
        double ldSum = ldArr.Skip(i - n).Take(n).Sum();
        pdi = hdSum / trSum * 100;
        mdi = ldSum / trSum * 100;
        double diff = Math.Abs(pdi - mdi);
        double sum = pdi + mdi;
        dx = diff / sum * 100;
        adx = sumDx / n;
        adxr = (adx + adxArr[i - 1]) / 2;
        pdiArr[i] = Math.Round(pdi, 3);
        mdiArr[i] = Math.Round(mdi, 3);
        dxArr[i] = Math.Round(dx, 3);
        adxArr[i] = Math.Round(adx, 3);
        adxrArr[i] = Math.Round(adxr, 3);
    }

    // 将计算结果添加到结果DataTable中
    for (int i = 0; i < dt.Rows.Count; i++)
    {
        DataRow row = resultDt.NewRow();
        row["日期"] = dt.Rows[i]["日期"];
        row["PDI"] = pdiArr[i];
        row["MDI"] = mdiArr[i];
        row["ADX"] = adxArr[i];
        row["ADXR"] = adxrArr[i];
        resultDt.Rows.Add(row);
    }

    return resultDt;
}

其中，n为DMI的周期，m为ADX的周期。计算过程中，先计算每日的TR、HD和LD，再根据n计算PDI、MDI、DX、ADX和ADXR。最后将计算结果添加到结果DataTable中，并返回该DataTable。

希望这个函数能够满足你的需求，如果有任何问题，欢迎随时向我提出。