Hello,

I have ploted the same functions in MATLAB and then with QwtPlot and the results are different. Could you tell me why and how to deal properly with complex numbers in QwtPlot?

Thank you

best regards,

Vitali

here is the definition of functions:
Qt Code: 
  1. complex<double> benchfunc_2_constr_1(complex<double> x){
  2. 						return (5.0 + sqrt(100.0 - pow(x - 5.0 ,2)));			// (-pow(x1-5,2) - pow(x2-5,2) +100) <=0
  3. 						}												// resp. y >= 5 + sqrt(100 - pow(x - 5,2))
  4.  
  5. 				complex<double> benchfunc_2_constr_2(complex<double> x){
  6. 						return (5.0 + sqrt(82.81 - pow(x - 6.0 ,2)));			// (-pow(x1-6,2) - pow(x2-5,2) - 82.81) <=0
  7. 						}												// resp. y <= 5 + sqrt(82,81 - pow(x - 6,2))
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here is the class which generates data for ploting the curves:
Qt Code: 
  1. class SimpleData: public QwtData
  2. {
  3.  
  4. public:
  5.     SimpleData( complex<double> (*b)(complex<double>), double rang1[2], double rang2[2], double step)
  6.     {
  7.     	constraintFunc = b;
  8.     	_step = step;
  9.     	rangeX[0]= rang1[0];	rangeX[1] = rang1[1];
  10.     	rangeY[0]= rang2[0];	rangeY[1] = rang2[1];
  11.     	range = (rangeX[1] - rangeX[0])/step;
  12.     	if(range<0){
  13.     		range = range *(-1);
  14.     	}
  15.     	d_size = size_t(range);
  16.     }
  17.  
  18.     virtual QwtData *copy() const
  19.     {
  20.         return new SimpleData(*this);
  21.     }
  22.  
  23.     virtual size_t size() const
  24.     {
  25.         return d_size;
  26.     }
  27.  
  28.     virtual double x(size_t i) const
  29.     {
  30.     	// here the array with x values will be produced
  31.     	return rangeX[0] + i*((rangeX[1]- rangeX[0])/range);
  32.     }
  33.  
  34.     virtual double y(size_t i) const
  35.     {
  36.     	complex<double> result = (*constraintFunc)(x(i));	// compute the y value
  37.  
  38.     	if(real(result) > rangeY[1]){	// if exceeds the max bound
  39.     		return rangeY[1];
  40.     	}
  41.     	else if(real(result) < rangeY[0]){ // if exceeds the min bound
  42.     		return rangeY[0];
  43.     	}
  44.     	else return real(result);	// return only the real value of complex number
  45.     }
  46. private:
  47.     size_t d_size;
  48.     double range;
  49.     double _step;
  50.     complex<double> (*constraintFunc)(complex<double>);	// function pointer for constraint function
  51. 	double rangeX[2];
  52. 	double rangeY[2];
  53. };
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somewhere in code the data for the curve is set with:
Qt Code: 
  1. curve1->setData(SimpleData((*ii).second, rangex1, rangex2, 0.05));
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and here the MATLAB code for comparison:

Qt Code: 
  1. [x1, x2] = meshgrid(13:1:100, 0:1:100);
  2. f = (x1 -10).^3 + (x2 - 20).^3;    % problem function
  3. g1 = @(x) sqrt(100 - (x-5).^2 ) + 5;            % constraint function 1
  4. g2 = @(x) sqrt(82.81 -(x-6).^2 ) +5;            % constraint function 2
  5.  
  6. t=13:0.1:100;
  7. y1 = g1(t);
  8. y2 = g2(t);
  9.  
  10.  
  11. figure
  12. subplot(1,2,1)
  13. surf(x1,x2,f);
  14. subplot(1,2,2)
  15. contour(x1,x2,f);
  16. hold on 
  17. plot(t, g1(t), 'r');
  18. plot(t, g2(t), 'y');
  19. hold off
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