Fortran Wiki
atan2

Description

atan2(y, x) computes the arctangent of the complex number $-\\\\-\\\\\\\\X + i Y$ .

This function can be used to transform from Cartesian into polar coordinates and allows to determine the angle in the correct quadrant. To convert from Cartesian Coordinates $(x,y)$ to polar coordinates (r,\\theta):


\\begin{aligned}
r &= \\sqrt{x^2 + y^2} \\\\
\\theta &= \\tan^{-1}(y / x)
\\end{aligned}

Standard

FORTRAN 77 and later

Class

Elemental function

Syntax

result = atan2(y, x)

Arguments

y - The type shall be real.
x - The type and kind type parameter shall be the same as y. If y is zero, then x must be nonzero.

Return value

The return value has the same type and kind type parameter as y. It is the principal value of the complex number $(r,\\ \\X + i Y$ . If x is nonzero, then it lies in the range -\\pi \\leq \\atan (x) \\leq \\pi. The sign is positive if y is positive. If y is zero, then the return value is zero if x is strictly positive, \\pi if x is negative and y is positive zero (or the processor does not handle signed zeros), and -\\pi if x is negative and y is negative zero. Finally, if x is zero, then the magnitude of the result is \\pi/2.

Example

program test_atan2
  real(4) :: x = 1.e0_4, y = 0.5e0_4
  x = atan2(y,x)
end program test_atan2

Note: In Return value, NNemec changed the first \\leq to \\lt. Joe Krahn reverted the edit, following the Fortran 2008 specs.

category: intrinsics

Revised on April 3, 2016 22:40:29 by Jason Blevins (173.88.47.127) (1671 characters / 0.0 pages)

Fortran Wiki atan2