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# /(+Number1, +Number2, -Result)

Evaluates the quotient Number1 / Number2 and unifies the resulting value with Result.

Number1
  A number.
Number2
  A number.
Result
  Output: float (or rational).

## Description

This predicate is used by the ECLiPSe compiler to expand evaluable arithmetic expressions. So the call to /(Number1, Number2, Result) is equivalent to

        Result is Number1 / Number2

which should be preferred for portability.

If both arguments are integers, then the result is of type float by default (coinciding with ISO-Prolog). This can be changed by switching the global flag 'prefer_rationals' to 'on': the result is then of rational type, and therefore precise. In practice, a better way to enforce a rational result is by explicitly converting one or both arguments to a rational before dividing, e.g. Z is rational(X)/Y.

The following table details the behaviour on zero-division, depending on the argument types. The exact result depends on the result's type ability to represent extreme values.

          -3 / 0                        -1.0Inf (negative infinity)
           0 / 0                        arithmetic exception
           3 / 0                         1.0Inf (positive infinity)

          -3.0 / 0.0                    -1.0Inf (negative infinity)
          -0.0 / 0.0                    arithmetic exception
           0.0 / 0.0                    arithmetic exception
           3.0 / 0.0                     1.0Inf (positive infinity)
          -3.0 / -0.0                    1.0Inf (positive infinity)
          -0.0 / -0.0                    arithmetic exception
           0.0 / -0.0                    arithmetic exception
           3.0 / -0.0                   -1.0Inf (negative infinity)

          rational(-3) / rational(0)    representation error
          rational( 0) / rational(0)    arithmetic exception
          rational( 3) / rational(0)    representation error

          breal(-3) / breal(0)          -1.0Inf__-1.0Inf (negative infinity)
          breal( 0) / breal(0)          -1.0Inf__1.0Inf (undefined)
          breal( 3) / breal(0)           1.0Inf__1.0Inf (positive infinity)

Dividing infinity by infinity yields the same result as 0/0.

In coroutining mode, if Number1 or Number2 are uninstantiated, the call to //3 is delayed until these variables are instantiated.

### Modes and Determinism

- /(+, +, -) is det

### Exceptions

(4) instantiation fault
  Number1 or Number2 is not instantiated (non-coroutining mode only).
(24) number expected
  Number1 or Number2 is not of a numeric type.
(20) arithmetic exception
  Illegal arithmetic operation: 0/0 or infinity/infinity

## Examples

    Success:
        Result is 10 / 2.		% gives Result = 5.0
        Result is 10 / -2.0.	% gives Result = -5.0
        Result is 9 / 12.		% gives Result = 0.75

        % with set_flag(prefer_rationals, on):
        Result is 9 / 12.		% gives Result = 3_4

    Error:
        Result is 2/0.              % arithmetic exception

## See Also

is / 2, get_flag / 2, set_flag / 2