Complex Numbers

Hi

I'm having a problem with complex numbers. I have an equation that I must use. However, most of the time the result is complex, and I think I just need the real part. This doesn't work:

Code:

#define sigma 0.3
#include <complex>

.....

complex<double> num;
double y = 0;

float x = ...just something

num = sqrt(-2.0f*sigma*sigma*log(1.0f - x)); //apparently a pc doesn't know 
                                                                       //how to do this
y = real(num);

I haven't found anything about how to do this. I printed out the variable y and it usually just shows "1.#QO", but I need the real part of the result of the equation.

Please tell me there is a way do to this...

Is this what you want?

Code:

#include <iostream>
#include <complex>

using namespace std;

const double sigma(0.3);

int main()
{
    double x = .3;

    complex<double> num = sqrt(-2.0 * sigma * sigma * log(1.0 - x));
    double y = num.real();
    cout << y << endl;
    
    return 0;
}

Yeah, except that still doesn't work. In the equation x can be between 0 and 100 (part of my assignment), so the result is usually complex, and I don't know how to handle it.


The complete program:

Code:

#include <iostream>
#include <ctime>
#include <fstream>
#include <complex>
#include <cmath>

using namespace std;

#define sigma 0.3f
#define pi 3.14159f
#define tab '\t'

void randomGenerator(float *& array, float a, float b, int count)
{
    array = new float[count];
    srand(time(NULL));
    
    for(int i = 0; i < count; i++)
    {
        array[i] = ((b-a)*((float)rand()/(float)RAND_MAX))+a;   
    }          
        //http://www.codeguru.com/forum/showthread.php?t=351834
}

int main()
{
    ofstream f_out;
    f_out.open("rayleigh.txt");
    f_out.precision(4);
    
    complex<double> num;
    double y = 0;
    float a, b;
    int count;
    bool option = 0;
    float * array;
    
    cout << "Enter the random number range(smallest number first): ";
    cin >> a >> b;
    cout << endl << "Enter the desired number of random numbers: ";
    cin >> count;
    cout << "Negate half of the numbers? (1 for yes): ";
    cin >> option;
    cout << endl << "Generating random numbers..." << endl;
    randomGenerator(array, a, b, count);
    
    for(int i = 0; i < count; i++)
    {
        num = sqrt(-2.0f*sigma*sigma*log(1.0f - array[i]));
        y = num.real();
     //   if(option == 1)
    //    {
    //         if(((float)rand()/(float)RAND_MAX) > 0.5f)
     //             y = -y;
     //   } 
        f_out << array[i] << tab << y << endl;
    }
    
    cout << "Rayleigh distribution output to rayleigh.txt. " << endl;
    cout << "Press any key to continue..." << endl;
    cin.get();
    cin.get();
    delete[] array;
    f_out.close();
    return 0;
}

To use the complex version of sqrt(), you will need to make the value into a complex number FIRST, then call sqrt(), e.g.

Code:

    complex<double> num = sqrt(complex<double>(-2.0 * sigma * sigma * log(1.0 - x), 0));

Otherwise, it will just call the regular sqrt(double) function, which of course doesn't understand how to deal with the negative value.

--
Mats