ATAN2 — Arctangent function#

ATAN2(Y, X)#

ATAN2(Y, X) computes the principal value of the argument function 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.

Parameters

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.

Returns

The return value has the same type and kind type parameter as Y. It is the principal value of the complex number X + i Y. If X is nonzero, then it lies in the range -pi le 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.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = ATAN2(Y, X)

Example:

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

Specific names:

Name	Argument	Return type	Standard
`ATAN2(X, Y)`	`REAL(4) X, Y`	`REAL(4)`	Fortran 77 and later
`DATAN2(X, Y)`	`REAL(8) X, Y`	`REAL(8)`	Fortran 77 and later

See also:

Alias: ATAN Degrees function: ATAN2D