title: Qt - QCustomPlot painting graph
body: <p>I have a problem with drawing the graph in QCustomPlot library. I would like to draw a logarithm graph but I use drawing on the interval &lt;-3;3>. Because logarithm is not defined from -3 to 0, I tried to do nothing while drawing on this interval.</p>
  
  <p>I have this code:</p>
  
  <pre><code>QVector&lt;double&gt; x(10001), y(10001);
  QVector&lt;double&gt; x1(10001), y1(10001);
  
  double t=-3; //cas
  double inkrement = 0.0006;
  for (int i=0; i&lt;10001; i++)//kvadraticka funkcia
  {
    x[i] = t;
    y[i] = (-1)*t*t-2;
    t+=inkrement;
  }
  
  int g=0;
  for(double l=-3;l&lt;3; l+=inkrement) {
     if(l&lt;=0.0) continue;
     else {
     //QMessageBox::warning(this, tr("note"), tr("l=%1\n").arg(l), QMessageBox::Ok);
     x1[g] = l;
     y1[g] = log10(l)/log10(exp(1.0));
     //QMessageBox::warning(this, tr("note"), tr("x1=%1\ny1=%2").arg(x1[g]).arg(y1[g]), QMessageBox::Ok);
     //break;
     g++;
     }
  }
  
  customPlot-&gt;addGraph();
  customPlot-&gt;graph(0)-&gt;setData(x, y);
  
  customPlot-&gt;addGraph();
  customPlot-&gt;graph(1)-&gt;setData(x1, y1);
  
  customPlot-&gt;xAxis-&gt;setLabel("x");
  customPlot-&gt;yAxis-&gt;setLabel("y");
  
  customPlot-&gt;xAxis-&gt;setRange(-3, 3);
  customPlot-&gt;yAxis-&gt;setRange(-10, 5);
  customPlot-&gt;replot();
  </code></pre>
  
  <p>where x1 and y1 are QVectors... But the graph is like the first point is in [0,0]. So I have then a line that connects point [0,0] with the logarithm graph and I dont know why :( 
  When I put l=0.0006 before the cycle, everything is OK. Can you help me with that please?</p>