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### 9.23 ATAN — Arctangent function

Description:

ATAN(X) computes the arctangent of X.

Standard:

Fortran 77 and later, for a complex argument and for two arguments Fortran 2008 or later

Class:

Elemental function

Syntax:
 RESULT = ATAN(X) RESULT = ATAN(Y, X)
Arguments:
 X The type shall be REAL or COMPLEX; if Y is present, X shall be REAL. Y The type and kind type parameter shall be the same as X.
Return value:

The return value is of the same type and kind as X. If Y is present, the result is identical to ATAN2(Y,X). Otherwise, it the arcus tangent of X, where the real part of the result is in radians and lies in the range -\pi/2 \leq \Re \atan(x) \leq \pi/2.

Example:
program test_atan
real(8) :: x = 2.866_8
x = atan(x)
end program test_atan

Specific names:
 Name Argument Return type Standard ATAN(X) REAL(4) X REAL(4) Fortran 77 and later DATAN(X) REAL(8) X REAL(8) Fortran 77 and later