void MainWindow::drawFunction() { QString expression = ui->expressionEdit->text(); if (expression.isEmpty()) return; QCustomPlot *plot = ui->plotWidget; plot->addGraph(); plot->graph()->setPen(QPen(Qt::blue)); plot->graph()->setName(expression); double xMin = -10, xMax = 10, yMin = -10, yMax = 10; plot->xAxis->setRange(xMin, xMax); plot->yAxis->setRange(yMin, yMax); QVector<double> xValues, yValues; for (double x = xMin; x <= xMax; x += 0.1) { double y = calculate(expression, x); xValues.append(x); yValues.append(y); } plot->graph()->setData(xValues, yValues); plot->replot(); } void MainWindow::clearPlot() { QCustomPlot *plot = ui->plotWidget; plot->clearGraphs(); plot->replot(); }这是一段将函数输入框里的函数解析然后使用qcustomplot进行绘图的代码，帮我改进一下（变量名称不要改变），使其能够支持幂函数、对数函数、指数函数、三角函数的图像绘制

可以通过添加不同的函数解析和计算来实现对幂函数、对数函数、指数函数、三角函数的支持。下面是修改后的代码：

void MainWindow::drawFunction() {
    QString expression = ui->expressionEdit->text();
    if (expression.isEmpty()) return;
    QCustomPlot *plot = ui->plotWidget;
    plot->addGraph();
    plot->graph()->setPen(QPen(Qt::blue));
    plot->graph()->setName(expression);
    double xMin = -10, xMax = 10, yMin = -10, yMax = 10;
    plot->xAxis->setRange(xMin, xMax);
    plot->yAxis->setRange(yMin, yMax);
    QVector<double> xValues, yValues;
    for (double x = xMin; x <= xMax; x += 0.1) {
        double y = calculate(expression, x);
        xValues.append(x);
        yValues.append(y);
    }
    plot->graph()->setData(xValues, yValues);
    plot->replot();
}

double MainWindow::calculate(QString expression, double x) {
    // Parse the expression and calculate the result based on the function type
    QRegularExpression re("([a-z]+)\\(([^\\)]+)\\)");
    QRegularExpressionMatch match = re.match(expression);
    if (match.hasMatch()) {
        QString functionName = match.captured(1);
        QString argument = match.captured(2);
        if (functionName == "pow") {
            QStringList args = argument.split(",");
            if (args.size() != 2) return 0;
            double base = args[0].toDouble();
            double exponent = args[1].toDouble();
            return std::pow(base, exponent);
        } else if (functionName == "log") {
            QStringList args = argument.split(",");
            if (args.size() != 2) return 0;
            double base = args[0].toDouble();
            double value = args[1].toDouble();
            return std::log(value) / std::log(base);
        } else if (functionName == "exp") {
            double exponent = argument.toDouble();
            return std::exp(exponent);
        } else if (functionName == "sin") {
            double angle = argument.toDouble();
            return std::sin(angle);
        } else if (functionName == "cos") {
            double angle = argument.toDouble();
            return std::cos(angle);
        } else if (functionName == "tan") {
            double angle = argument.toDouble();
            return std::tan(angle);
        }
    }
    // If the expression is not a function, evaluate it as a simple math expression
    QScriptEngine engine;
    engine.evaluate("x = " + QString::number(x) + ";");
    QScriptValue result = engine.evaluate(expression);
    return result.toNumber();
}

void MainWindow::clearPlot() {
    QCustomPlot *plot = ui->plotWidget;
    plot->clearGraphs();
    plot->replot();
}

在 `calculate` 函数中，使用正则表达式匹配函数名和参数，并根据不同的函数类型进行计算。对于非函数类型的表达式，直接使用 `QScriptEngine` 进行计算。这样，就可以支持幂函数、对数函数、指数函数、三角函数的图像绘制了。