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# atan(+Number, -Result)

Evaluates the trigonometric function atan(Number) and unifies the resulting
value with Result.
*Number*
- A number.
*Result*
- A variable, 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).
*(5) type error *
- Result is a number but not a float or breal
*(24) number expected *
- Number is not of a numeric type.
*(24) number expected *
- Result is neither a number nor a variable.

## Examples

Success:
atan(0.0, 0.0).
atan(1.0, Result). (gives Result = 0.785398)
atan(-8, Result). (gives Result = -1.44644)
Fail:
atan(1, 0.0).
Error:
atan(A, 6.0). (Error 4).
atan(1.55741, 1). (Error 5).
atan(1 + 0.55741, 1.0). (Error 24).
atan(5, r). (Error 24).

## See Also

is / 2