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# ln(+Number, -Result)

Evaluates the natural logarithm ln(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 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

- ln(+, -) is det

### 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:
        Result is ln(2.0).          % gives Result = 0.693147
        Result is ln(1).            % gives Result = 0.0

    Error:
        Result is ln(-2).           % arithmetic exception
        Result is ln(0).            % arithmetic exception

## See Also

is / 2