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# atan(+Number, -Result)

Evaluates the trigonometric function atan(Number) and unifies the resulting value with Result.

Number
  A number.
Result
  Output: float or breal.

## Description

This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to atan(Number, Result) is equivalent to

        Result is atan(Number)

which should be preferred for portability.

In coroutining mode, if Number is uninstantiated, the call to atan/2 is delayed until this variable is instantiated.

### Modes and Determinism

- atan(+, -) is det

### Exceptions

(4) instantiation fault
  Number is not instantiated (non-coroutining mode only).
(24) number expected
  Number is not of a numeric type.

## Examples

        Result is atan(0.0).		% gives Result = 0.0
        Result is atan(1.0).		% gives Result = 0.785398
        Result is atan(-8).			% gives Result = -1.44644

## See Also

is / 2