def _(expr, assumptions): """ * Unbounded ** NonZero -> Unbounded * Bounded ** Bounded -> Bounded * Abs()<=1 ** Positive -> Bounded * Abs()>=1 ** Negative -> Bounded * Otherwise unknown """ if expr.base == E: return ask(Q.finite(expr.exp), assumptions) base_bounded = ask(Q.finite(expr.base), assumptions) exp_bounded = ask(Q.finite(expr.exp), assumptions) if base_bounded is None and exp_bounded is None: # Common Case return None if base_bounded is False and ask(Q.extended_nonzero(expr.exp), assumptions): return False if base_bounded and exp_bounded: return True if (abs(expr.base) <= 1) == True and ask(Q.extended_positive(expr.exp), assumptions): return True if (abs(expr.base) >= 1) == True and ask(Q.extended_negative(expr.exp), assumptions): return True if (abs(expr.base) >= 1) == True and exp_bounded is False: return False return None
def _(expr, assumptions): """ Return True if expr is bounded, False if not and None if unknown. Truth Table: +-------+-----+-----------+-----------+ | | | | | | | B | U | ? | | | | | | +-------+-----+---+---+---+---+---+---+ | | | | | | | | | | | |'+'|'-'|'x'|'+'|'-'|'x'| | | | | | | | | | +-------+-----+---+---+---+---+---+---+ | | | | | | B | B | U | ? | | | | | | +---+---+-----+---+---+---+---+---+---+ | | | | | | | | | | | |'+'| | U | ? | ? | U | ? | ? | | | | | | | | | | | | +---+-----+---+---+---+---+---+---+ | | | | | | | | | | | U |'-'| | ? | U | ? | ? | U | ? | | | | | | | | | | | | +---+-----+---+---+---+---+---+---+ | | | | | | | |'x'| | ? | ? | | | | | | | +---+---+-----+---+---+---+---+---+---+ | | | | | | ? | | | ? | | | | | | +-------+-----+-----------+---+---+---+ * 'B' = Bounded * 'U' = Unbounded * '?' = unknown boundedness * '+' = positive sign * '-' = negative sign * 'x' = sign unknown * All Bounded -> True * 1 Unbounded and the rest Bounded -> False * >1 Unbounded, all with same known sign -> False * Any Unknown and unknown sign -> None * Else -> None When the signs are not the same you can have an undefined result as in oo - oo, hence 'bounded' is also undefined. """ sign = -1 # sign of unknown or infinite result = True for arg in expr.args: _bounded = ask(Q.finite(arg), assumptions) if _bounded: continue s = ask(Q.extended_positive(arg), assumptions) # if there has been more than one sign or if the sign of this arg # is None and Bounded is None or there was already # an unknown sign, return None if sign != -1 and s != sign or \ s is None and (s == _bounded or s == sign): return None else: sign = s # once False, do not change if result is not False: result = _bounded return result