Lahey/Fujitsu Fortran

# ATAN2 Function

### Description

The ATAN2 function returns the arctangent of y/x, expressed as radians. The ATAN2 function is able to return a greater range of values than the ATAN function, because it considers the sign of x and y.

```Syntax

ATAN2 (y, x)
```

### Arguments

y is an INTENT(IN) scalar or array of type REAL.

x is INTENT(IN) and of the same kind as y. If y is an array, x must be an array conformable to y. If y is zero, x cannot be zero.

### Result

The result is of the same kind as y. Its value is a REAL representation, expressed in radians, of the principal value of the argument of the complex number x + iy. The result falls within the range -Π < x ≤ Π .

If y is positive, the result is positive. If y is negative, the result is negative. If y is zero and x > 0 , the result is zero. If y is zero and x < 0 , the result is pi. If x is zero, the result is a representation of the value Π/2 having the sign of y.

```Example
real :: y=1.,x=1.
write(*,*) atan2(y,x)   ! writes 0.78539818
write(*,*) atan2(-y,x)  ! writes -0.78539818
write(*,*) atan2(y,-x)  ! writes 2.3561945
write(*,*) atan2(-y,-x) ! writes -2.3561945
write(*,*) atan2(0.,x)  ! writes 0.0000000
write(*,*) atan2(0.,-x) ! writes 3.1415927
write(*,*) atan2(y,0.)  ! writes 1.5707963
write(*,*) atan2(-y,0.) ! writes -1.5707963
```