Namespaces
Variants

    std::arg(std::complex)

    From cppreference.com
     
    C++
     
    Numerics library
     
    std::complex
     
    Defined in header <complex>
    template< class T > T arg( const std::complex<T>& z );
    		 (1)
    Additional overloads (since C++11)
    Defined in header <complex>
    (A)
    float arg( float f ); double arg( double f ); long double arg( long double f );
    		 (until C++23)
    template< class FloatingPoint > FloatingPoint arg( FloatingPoint f );
    		 (since C++23)
    template< class Integer > double arg( Integer i );
    		 (B)
    1) Calculates the phase angle (in radians) of the complex number z.
    A,B) Additional overloads are provided for all integer and floating-point types, which are treated as complex numbers with zero imaginary component.
    		 (since C++11)

    Parameters

    z - complex value
    f - floating-point value
    i - integer value

    Return value

    1) std::atan2(std::imag(z), std::real(z)). If no errors occur, this is the phase angle of z in the interval [−π; π].
    A) Zero if f is positive or +0, π if f is negative or -0, NaN otherwise.
    B) Zero if i is non-negative, π if it is negative.

    Notes

    See More

    The additional overloads are not required to be provided exactly as (A,B). They only need to be sufficient to ensure that for their argument num:

    • If num has a standard(until C++23) floating-point type T, then std::arg(num) has the same effect as std::arg(std::complex<T>(num)).
    • Otherwise, if num has an integer type, then std::arg(num) has the same effect as std::arg(std::complex<double>(num)).

    Example

    Run this code
    #include <complex>
#include <iostream>

int main() 
{
    std::complex<double> z1(1, 0);
    std::complex<double> z2(0, 0);
    std::complex<double> z3(0, 1);
    std::complex<double> z4(-1, 0);
    std::complex<double> z5(-1, -0.0);
    double f = 1.;
    int i = -1;

    std::cout << "phase angle of " << z1 << " is " << std::arg(z1) << '\n'
              << "phase angle of " << z2 << " is " << std::arg(z2) << '\n'
              << "phase angle of " << z3 << " is " << std::arg(z3) << '\n'
              << "phase angle of " << z4 << " is " << std::arg(z4) << '\n'
              << "phase angle of " << z5 << " is " << std::arg(z5) << " "
                 "(the other side of the cut)\n"
              << "phase angle of " << f << " is " << std::arg(f) << '\n'
              << "phase angle of " << i << " is " << std::arg(i) << '\n';

}

    Output: 

    phase angle of (1,0) is 0
phase angle of (0,0) is 0
phase angle of (0,1) is 1.5708
phase angle of (-1,0) is 3.14159
phase angle of (-1,-0) is -3.14159 (the other side of the cut)
phase angle of 1 is 0
phase angle of -1 is 3.14159

    See also

    		 returns the magnitude of a complex number
    (function template) [edit]
    		constructs a complex number from magnitude and phase angle
    (function template) [edit]
    (C++11)(C++11)
    		 arc tangent, using signs to determine quadrants
    (function) [edit]
    		applies the function std::atan2 to a valarray and a value
    (function template) [edit]
    C documentation for carg