X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=src%2FComparisons.hs;h=d033159f23f827fa3776ca2c6dd2ac775780af91;hb=638f544b522157f83b075e07a70b2f106e01ec68;hp=506ebab8217b8c46cda4bf2b8ee7fe636c619cf2;hpb=28710758dac0a1241911c6ba296b0685b877b5e3;p=spline3.git

diff --git a/src/Comparisons.hs b/src/Comparisons.hs
index 506ebab..d033159 100644
--- a/src/Comparisons.hs
+++ b/src/Comparisons.hs
@@ -1,12 +1,24 @@
+-- | 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
 
+-- | A tiny margin of error.
+theta :: Double
+theta = 0.0000000000001
+
+-- | x almost equals y if x is within 'theta' of y.
+nearly_equals :: Double -> Double -> Bool
+nearly_equals x y = (abs (x - y)) < theta
+
+-- | Nearly greater-than or equal-to.
+nearly_ge :: Double -> Double -> Bool
+x `nearly_ge` y = (x > y) || (x `nearly_equals` y)
 
 -- | x almost equals y if x is within 'epsilon' of y.
 almost_equals :: Double -> Double -> Bool
@@ -17,12 +29,26 @@ infix 4 ~=
 (~=) = 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)