+-- | Functions for comparing 'Double' values.
module Comparisons
where
-- | epsilon is the value that will be used in all tests that require
--- some measure of "closeness." Increasing it will make those tests
--- more tolerant.
+-- some measure of \"closeness.\" Increasing it will make those
+-- tests more tolerant.
epsilon :: Double
epsilon = 0.0001
(~=) = almost_equals
+-- | Like 'almost_equals', except much more tolerant. The difference
+-- between the two arguments must be less than one percent of the sum
+-- of their magnitudes.
+kinda_equals :: Double -> Double -> Bool
+kinda_equals x y =
+ (abs (x - y)) < threshold
+ where
+ threshold = ((abs x) + (abs y)) / 100.0
+
+infix 4 ~~=
+(~~=) :: Double -> Double -> Bool
+(~~=) = kinda_equals
+
+
-- | x is very positive if it is 'epsilon' greater than zero.
very_positive :: Double -> Bool
very_positive x = x - epsilon > 0
--- | Takes a list of Doubles and returns the ones which are not very
+-- | Takes a list of 'Double' and returns the ones which are not very
-- positive.
non_very_positive_entries :: [Double] -> [Double]
non_very_positive_entries = filter (not . very_positive)