Is there anything wrong with std::pow?

[Peng Yu]

Hi,

The output of the following program is
(-27.7128,16) (-9.09495e-12,32768)

Obviously, y*y*y is not equal to x, even the magnitude is off. I'm
wondering what is wrong here.

Thanks,
Peng

#include <complex>
#include <iostream>

int main () {
std::complex<doublex(2, 2);
std::complex<doubley = std::pow(x, 1/.3);
std::cout << y << " " << y * y * y << std::endl;
}

[Peng Yu]

On Sep 9, 8:29 pm, "Alf P. Steinbach" <[e-mail]:

* Peng Yu:

Hi,

The output of the following program is
(-27.7128,16) (-9.09495e-12,32768)

Obviously, y*y*y is not equal to x, even the magnitude is off. I'm
wondering what is wrong here.

Thanks,
Peng

#include <complex>
#include <iostream>

int main () {
std::complex<doublex(2, 2);
std::complex<doubley = std::pow(x, 1/.3);
std::cout << y << " " << y * y * y << std::endl;
}

The second argument to pow.

I don't quite understand what you mean. Would you please be more
specific?

Thanks,
Peng

[Sjouke Burry]

Peng Yu wrote:

On Sep 9, 8:29 pm, "Alf P. Steinbach" <[e-mail]:

>* Peng Yu:

>>Hi,
The output of the following program is
(-27.7128,16) (-9.09495e-12,32768)
Obviously, y*y*y is not equal to x, even the magnitude is off. I'm
wondering what is wrong here.
Thanks,
Peng
#include <complex>
#include <iostream>
int main () {
std::complex<doublex(2, 2);
std::complex<doubley = std::pow(x, 1/.3);
std::cout << y << " " << y * y * y << std::endl;
}

The second argument to pow.

I don't quite understand what you mean. Would you please be more
specific?

Thanks,
Peng

1/.3 equals 3.333333, perhaps you meant 1./3.

[Peng Yu]

On Sep 9, 9:35 pm, Sjouke Burry <[e-mail]>
wrote:

Peng Yu wrote:

On Sep 9, 8:29 pm, "Alf P. Steinbach" <[e-mail]:

* Peng Yu:

>Hi,
The output of the following program is
(-27.7128,16) (-9.09495e-12,32768)
Obviously, y*y*y is not equal to x, even the magnitude is off. I'm
wondering what is wrong here.
Thanks,
Peng
#include <complex>
#include <iostream>
int main () {
std::complex<doublex(2, 2);
std::complex<doubley = std::pow(x, 1/.3);
std::cout << y << " " << y * y * y << std::endl;
}
The second argument to pow.

I don't quite understand what you mean. Would you please be more
specific?

Thanks,
Peng

1/.3 equals 3.333333, perhaps you meant 1./3.

I'm sorry that I could pinpoint it. Thank you.

Peng