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Thread: Plot x^2 curve

  1. #1
    Join Date
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    Question Plot x^2 curve

    Hi all,

    I have this code to plot the x^2 curve:

    Qt Code:
    1. // add curves
    2. QwtPlotCurve *curve1 = new QwtPlotCurve("Graph 1");
    3.  
    4. //set curve color
    5. curve1->setPen(QPen(Qt::red, 2));
    6.  
    7. // add curves
    8. curve1->attach(ui->qwtPlotWidget);
    9.  
    10. const int MAX_VALUES = 100;
    11. double x[2*MAX_VALUES], y1[2*MAX_VALUES];// x and y values
    12. for (int i (-MAX_VALUES); i < MAX_VALUES; i++)
    13. {
    14. x[i] = i;
    15. y1[i] = i*i;
    16. }
    17.  
    18. // copy the data into the curves
    19. curve1->setSamples(x, y1, 2*MAX_VALUES);
    20.  
    21. // finally, refresh the plot
    22. ui->qwtPlotWidget->replot();
    To copy to clipboard, switch view to plain text mode 

    But I get this strange plot:


    What's wrong?

    Regards.

  2. #2
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    Default Re: Plot x^2 curve

    You are definitely missing "=" in line #12. x[-100..-1] and y[-100..-1] likely point to some garbage as well.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  3. #3
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    Default Re: Plot x^2 curve

    Can you put the right code please?

    Regards.

  4. #4
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    Default Re: Plot x^2 curve

    Qt Code:
    1. for(int i=0;i<MAX_VALUES*2;++i) {
    2. x[i] = -MAX_VALUES+i;
    3. y1[i] = x[i]*x[i];
    4. }
    To copy to clipboard, switch view to plain text mode 
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  5. #5
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    Default Re: Plot x^2 curve

    Thank you!

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