bnum 0.3

Bounded numbers

Bounded numbers were first conceptualized by Chris Crawford, and introduced in his book, Chris Crawford on Interactive Storytelling.

The basic idea of bounded numbers is to force the real number range into the bounded range of -1.0 < b < 1.0, with limits at -1.0 and 1.0, with the whole range observing a bell curve distribution.

A real number can be converted to a bounded number like so:

def _bind(unbounded_number: Union[float, int]) -> float:
    """Transform an unbounded number into an bounded number."""
    if unbounded_number > 0.0:
        return 1.0 - (1.0 / (1.0 + unbounded_number))
    else:
        return (1.0 / (1.0 - unbounded_number)) - 1.0

A bounded number may be transformed back to an unbounded number (with rounding errors) like so:

def _unbind(bounded_number: float) -> float:
  """Transform a bounded number into an unbounded number."""
  if bounded_number > 0.0:
      return (1.0 / (1.0 - bounded_number)) - 1.0
  else:
      return 1.0 - (1.0 / (1.0 + bounded_number))

Note that in the world of bounded numbers, from ten on up, the number of places beyond 1 roughly corresponds to the number of nines. That is:

• 10 ~= 0.9

• 100 ~= 0.99

• 1000 ~= 0.999

• etc.

Note also that the journey from unbounded to bounded will result in rounding errors. The larger the unbounded number, the larger the round-trip deviation.

Instantiating

Use the bnum(x) constructor (or its alias, b(x)) to make a bounded number from a float in the range -1.0 < x < 1.0.

Use bind(x) to bind an arbitrary real number.

Blending, Amplifying, Suppressing

Bounded numbers may be manipulated using the unique blend() function, which combines two bounded numbers with an optional weight. Without a weight, blend(x, y) finds the midpoint between x and y. A non-zero weight pushes the midpoint up or down accordingly.

The bnum type also has three blending shortcuts:

• x.blend(y, weight=0.0): equivalent of blend(x, y, weight).

• x.amplify(weight=0.0): scale x away from 0.

• x.suppress(weight=0.0): scale x towards 0.