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### 6.22 ATAN2 — Arctangent function

Description:
ATAN2(Y,X) computes the arctangent of the complex number X + i Y.
Standard:
F77 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 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 positive and \pi if X is negative. 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

Specific names:

 Name Argument Return type Standard DATAN2(X) REAL(8) X REAL(8) F77 and later