# Fortran Wiki atan

## 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 $-\pi / 2 \leq \mathop{Re}{\atan(x)} \leq \pi / 2$.

## Example

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