[ Arithmetic | Reference Manual | Alphabetic Index ]

# sgn(+Number, -Result)

Unifies Result with the sign of Number which is either -1, 0 or 1.

Number
  A number.
Result
  Output: an integer.

## Description

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

        Result is sgn(Number)

which should be preferred for portability.

sgn/2 gives the integer -1 if Number is negative, 0 if it is zero and 1 if it is greater than zero. It is always true that

        X =:= sgn(X) * abs(X)

Caution: this operation does not distinguish between +0.0 and -0.0. See copysign/3 for an alternative.

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

### Modes and Determinism

- sgn(+, -) 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 sgn(42).		% gives Result = 1
        Result is sgn(-5).		% gives Result = -1
        Result is sgn(-6.2).	% gives Result = -1
        Result is sgn(0.0).		% gives Result = 0
        Result is sgn(-0.0).	% gives Result = 0

## See Also

is / 2, abs / 2, copysign / 3