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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

### 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