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# ln(+Number, -Result)

Evaluates the natural logarithm ln(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 ln(Number, Result) is equivalent
to
Result is ln(Number)

which should be preferred for portability.
In coroutining mode, if Number is uninstantiated, the call to ln/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.
*(20) arithmetic exception *
- Illegal arithmetic operation: Number is 0 or less.

## Examples

Success:
ln(2.0, Result). (gives Result = 0.693147)
ln(1, Result). (gives Result = 0.0)
Fail:
ln(1, 1.0).
ln(1, 0).
ln(1, r).
Error:
ln(A, 6.0). (Error 4).
ln(-2, Result). (Error 20).
ln(0, Result). (Error 20).
ln(4 + 2, 1.79176). (Error 24).

## See Also

is / 2