atan2(y, x): ArcTangent

Arctangent function or inverse tangent function.

Declaration

Syntax

retval = atan2(y, x)
elemental real(p) function atan2(y, x)

Arguments

y the input value is the imaginary part of the complex expression

$x+iy$

x the input value, must be real part of the complex expression.

Return values

The returned value has the kind and TYPE as of the input value y. The principal value of the argument function of the complex expression $x+iy$ is returned.

Description

atan2(y, x) computes the principal value of the argument function of the complex expression $x+iy$. This is used to transform from cartesian into polar coordinates and allows to determine the angle in the correct quadrant.

It is also represented as:

$ta{n}^{-1}(\frac{y}{x})$

If x is nonzero, the result lies in the range:

$-\pi <=atan(x)<=\pi$

The sign is positive if y is positive.

If y is zero and x is strictly positive, then the result is 0.

If x is negative and y is positive zero, then the result is $\pi$.

If x is negative and y is negative zero, then the result is $-\pi$.

If x is zero, then the magnitude of the result is $\frac{\pi }{2}$.

If y is negative real zero, the result is $\frac{-\pi }{2}$.

Types

Supported argument type is real.

interface atan2
    module procedure satan2, datan2
end interface

contains

interface
    elemental real(sp) function satan2(y, x)
    real(sp), intent(in) :: y, x
    end function

    elemental real(dp) function datan2(y, x)
    real(dp), intent(in) :: y, x
    end function

end interface

Examples

program intrinsics_atan2
    implicit none
    print *, atan2(2.679676, 1.0)
end program

Result:

0.699521642

See Also