Next: ATAND, Previous: ASSOCIATED, Up: Intrinsic Procedures [Contents][Index]

### 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`shall be of the same type and kind 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 *See also*: