## ATAN intrinsic function

### Standard: F77 F90 F95 F2003 F2008 Example program

### ＜Syntax＞

ATAN ( X )

or ATAN ( Y, X )

X : Real or Complex;

Y : Conformable with X, same type and kind as X, which must be Real if Y is present;
the NAG Fortran Compiler also permits Y to have a different kind (this is non-standard);

Result : Same type as X, with kind the same as that of X+Y.

### ＜Semantics＞

The value of the result is an approximation to the arc tangent of X, in radians.
Like many intrinsic functions, this is **elemental**; the result has the same shape as X, with the operation being applied elementwise.

If X is of type Real, the result is in radians in the range −π/2≤ATAN(X)≤π/2. If X is of type Complex, the real part of the result is in radians, in the range −π/2≤REAL(ATAN(X))≤π/2.

The 2-argument form, ATAN ( Y, X ), is identical to ATAN2 ( Y, X ).

### ＜Related＞

ATAN2 intrinsic function, ATANH intrinsic function, TAN intrinsic function