用Qt计算多个坐标的方差并生成柱状图

要计算多个坐标的方差并生成柱状图，可以使用Qt的QChart和QBarSeries等类库来实现。

下面是一个使用Qt实现的计算函数和生成柱状图的示例代码：

#include <QApplication>
#include <QChartView>
#include <QList>
#include <QPointF>
#include <QtCharts/QBarCategoryAxis>
#include <QtCharts/QBarSeries>
#include <QtCharts/QBarSet>
#include <QtCharts/QChart>
#include <QtCharts/QValueAxis>

using namespace QtCharts;

double calculateVariance(const QList<QPointF>& coords)
{
    if (coords.isEmpty())
        return -1;

    double sumX = 0, sumY = 0;
    for (const QPointF& coord : coords) {
        sumX += coord.x();
        sumY += coord.y();
    }

    double meanX = sumX / coords.size();
    double meanY = sumY / coords.size();

    double sumSqrDiff = 0;
    for (const QPointF& coord : coords) {
        double diffX = coord.x() - meanX;
        double diffY = coord.y() - meanY;
        double sqrDiff = diffX * diffX + diffY * diffY;
        sumSqrDiff += sqrDiff;
    }

    return sumSqrDiff / coords.size();
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    // 生成坐标数据
    QList<QPointF> coords;
    coords.append(QPointF(1, 2));
    coords.append(QPointF(3, 4));
    coords.append(QPointF(5, 6));
    coords.append(QPointF(7, 8));
    coords.append(QPointF(9, 10));

    // 计算方差
    double variance = calculateVariance(coords);

    // 生成柱状图
    QBarSet *set = new QBarSet("Variance");
    *set << variance;

    QBarSeries *series = new QBarSeries();
    series->append(set);

    QChart *chart = new QChart();
    chart->addSeries(series);
    chart->setTitle("Variance of Coords");

    QBarCategoryAxis *axisX = new QBarCategoryAxis();
    chart->addAxis(axisX, Qt::AlignBottom);
    axisX->setTitleText("Coords");

    QValueAxis *axisY = new QValueAxis();
    chart->addAxis(axisY, Qt::AlignLeft);
    axisY->setTitleText("Variance");

    series->attachAxis(axisX);
    series->attachAxis(axisY);

    QChartView *chartView = new QChartView(chart);
    chartView->setRenderHint(QPainter::Antialiasing);

    chartView->show();

    return a.exec();
}

这个示例代码首先生成了一个包含5个坐标点的QList<QPointF>类型的数据结构，然后调用calculateVariance函数计算方差。接着使用QChart和QBarSeries等类库生成柱状图，将方差值作为数据添加到柱状图中，并设置x轴和y轴的标题。最后将柱状图显示出来。