Написать приложение, которое строит график математической функции y=f(x)

ui->centralWidget->graph(0)->setData(vx,vy);

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "vect.h"
 
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
newAct = new QAction(tr("&Новый"), this);
fileMenu = this->menuBar()->addMenu(tr("&Файл"));
fileMenu->addAction(newAct);
connect(newAct, SIGNAL(triggered()), this, SLOT(newFile()));
}
 
void MainWindow::newFile()
{
ui->centralWidget->addGraph();
ui->centralWidget->graph(0)->setData(vx,vy);
 
ui->centralWidget->xAxis->setLabel("Ось x");
ui->centralWidget->xAxis->setRange(0,n); //1
ui->centralWidget->yAxis->setLabel("f(x)");
ui->centralWidget->yAxis->setRange(-1,1);
 
ui->centralWidget->replot();
}
 
MainWindow::~MainWindow()
{
delete ui;
}

ui->centralWidget->graph(0)->setData(QVector<double>::fromStdVector(vx),fromStdVector(vy);

#include <QApplication>
#include <QMainWindow>
#include "qcustomplot.h"
#define _USE_MATH_DEFINES
#include <cmath>
 
 
double f(double x)
{
    double t = fabs(x) * fabs( sin(M_PI*x/2 + 1) );
    return x*x/sin(x/4*M_PI) + exp(log(t));
}
 
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QMainWindow w;
 
    QCustomPlot *cp = new QCustomPlot();
    w.setCentralWidget(cp);
    w.resize(800, 600);
 
    const double x1 = -10, x2 = 20, dx = 0.02;
    const int n = (x2-x1)/dx + 1;
 
    QVector<double> vx(n), vy(n);
    for(int i=0; i<n; i++)
    {
        double x=x1+dx*i;
        vx[i]=x;
        vy[i]=f(x);
    }
 
    cp->addGraph();
    cp->graph(0)->setData(vx, vy);
 
    cp->xAxis->setLabel("Ось x");
    cp->xAxis->setRange(x1, x2); //1
    cp->yAxis->setLabel("f(x)");
    cp->yAxis->setRange(-1,1);
 
    w.show();
 
    return a.exec();
}

QPrinter printer(QPrinter::ScreenResolution);
  printer.setOutputFileName(fileName);
  printer.setOutputFormat(QPrinter::PdfFormat);
  printer.setColorMode(QPrinter::Color);
  printer.printEngine()->setProperty(QPrintEngine::PPK_Creator, pdfCreator);
  printer.printEngine()->setProperty(QPrintEngine::PPK_DocumentName, pdfTitle);