-1.#IND in output???

Hi, what does this output mean?

Code:

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Discriminant = sqrtf(-16) or -1.#INDi

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Program code is as follows:

Code:

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cout << "Discriminant = sqrtf(" << discriminant << ") or ";
        d1 = sqrtf(discriminant);
        cout << d1 << "i" << endl << endl;

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Thanks a lot!

It means that the sqrt() of discriminant could not be calculated properly. The square root of negative numbers is not defined.

Of course, you could always use

Code:

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sqrt(fabs(discriminant))

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As for a more technical description of why it's "-1.#INDi" . . . I'm not entirely sure, but I'd guess that perhaps the trailing "i" means it's an imaginary number, which is what you get when you sqrt() a negative number. Google for more info.

http://www.randelshofer.ch/fhw/gri/float.html
#IND stands for indefinite.
Other things you can get from time to time are #INF and #NAN.

> I'm not entirely sure, but I'd guess that perhaps the trailing "i" means it's an imaginary number
Nah, that's just the trailing i in the cout statement.

Hi..

Thanks dwks and Salem.. what you guys said made a lot of sense. It was the first time I have encountered that -1.#IND and now, at least I have an idea of what it stands for.

Yes, the i came from the cout statement. However, I am trying to get the formula for the square root of the discriminant. Suppose, discriminant is equal to -16. Answer should be 4. How do I efficiently write the formula?

Any ideas? I will experiment on the fabs function.

Thanks guys..

Quote:

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However, I am trying to get the formula for the square root of the discriminant. Suppose, discriminant is equal to -16. Answer should be 4. How do I efficiently write the formula?

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Have you considered using the std::complex class template from <complex>? For example:

Code:

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#include <iostream>
#include <complex>

template<typename T>
void print(std::ostream& out, const std::complex<T>& x);

int main()
{
    std::complex<double> x(-16);
    std::cout << "sqrt(";
    print(std::cout, x);
    std::cout << ") = ";
    print(std::cout, sqrt(x));
    std::cout << std::endl;
}

template<typename T>
void print(std::ostream& out, const std::complex<T>& x)
{
    std::ios::fmtflags old_flags = out.flags();
    out << x.real() << std::showpos << x.imag() << "i";
    out.flags(old_flags);
}

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