
sgn(+Number, -Result)

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



Arguments
   Number              A number.
   Result              A variable or an integer.

Type
   Arithmetic

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)

   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 --- Number is not instantiated (non-coroutining mode only).
     5 --- Result is a non-integer number.
    24 --- Number is not of a numeric type.
    24 --- Result is neither a number nor a variable.

Examples
   
Success:
      sgn(42, 1).
      sgn(-5, Result).             (gives Result = -1)
      sgn(-6.2, Result).           (gives Result = -1)
      sgn(0.0, 0).
Fail:
      sgn(1, 0).
Error:
      sgn(A, 6).                   (Error 4).
      sgn(1, 1.0).                 (Error 5).
      sgn(4 + 2, 6).               (Error 24).
      sgn(1, r).                   (Error 24).





See Also
   is / 2
