atan(x) computes the arctangent of x.
FORTRAN 77 and later, alias for atan2 in Fortran 2008 and later
result = atan(x)
The return value is of type real and it lies in the range −π/2≤atan(x)≤π/2.
real(8) :: x = 2.866_8
x = atan(x)
end program test_atan