how to plot curves with complex numbers?

[rambo83]

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:

complex<double> benchfunc_2_constr_1(complex<double> x){
return (5.0 + sqrt(100.0 - pow(x - 5.0 ,2))); // (-pow(x1-5,2) - pow(x2-5,2) +100) <=0
} // resp. y >= 5 + sqrt(100 - pow(x - 5,2))

complex<double> benchfunc_2_constr_2(complex<double> x){
return (5.0 + sqrt(82.81 - pow(x - 6.0 ,2))); // (-pow(x1-6,2) - pow(x2-5,2) - 82.81) <=0
} // resp. y <= 5 + sqrt(82,81 - pow(x - 6,2))

here is the class which generates data for ploting the curves:

class SimpleData: public QwtData
{

public:
SimpleData( complex<double> (*b)(complex<double>), double rang1[2], double rang2[2], double step)
{
constraintFunc = b;
_step = step;
rangeX[0]= rang1[0]; rangeX[1] = rang1[1];
rangeY[0]= rang2[0]; rangeY[1] = rang2[1];
range = (rangeX[1] - rangeX[0])/step;
if(range<0){
range = range *(-1);
}
d_size = size_t(range);
}

virtual QwtData *copy() const
{
return new SimpleData(*this);
}

virtual size_t size() const
{
return d_size;
}

virtual double x(size_t i) const
{
// here the array with x values will be produced
return rangeX[0] + i*((rangeX[1]- rangeX[0])/range);
}

virtual double y(size_t i) const
{
complex<double> result = (*constraintFunc)(x(i)); // compute the y value

if(real(result) > rangeY[1]){ // if exceeds the max bound
return rangeY[1];
}
else if(real(result) < rangeY[0]){ // if exceeds the min bound
return rangeY[0];
}
else return real(result); // return only the real value of complex number
}
private:
size_t d_size;
double range;
double _step;
complex<double> (*constraintFunc)(complex<double>); // function pointer for constraint function
double rangeX[2];
double rangeY[2];
};

somewhere in code the data for the curve is set with:

curve1->setData(SimpleData((*ii).second, rangex1, rangex2, 0.05));

and here the MATLAB code for comparison:


[x1, x2] = meshgrid(13:1:100, 0:1:100);
f = (x1 -10).^3 + (x2 - 20).^3; % problem function
g1 = @(x) sqrt(100 - (x-5).^2 ) + 5; % constraint function 1
g2 = @(x) sqrt(82.81 -(x-6).^2 ) +5; % constraint function 2

t=13:0.1:100;
y1 = g1(t);
y2 = g2(t);


figure
subplot(1,2,1)
surf(x1,x2,f);
subplot(1,2,2)
contour(x1,x2,f);
hold on
plot(t, g1(t), 'r');
plot(t, g2(t), 'y');
hold off

[rambo83]

to define how the curves are "different" in MATLAB and QwtPlot: they look very similar if you not zoom in, but if you do, then you can see the difference, namely the curves intersect differently at x1 about 14...