X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=src%2FComparisons.hs;h=3bf4e246bcfba473634b255fb1befb8187a84b8f;hb=cc42825a4df8226f217e59e852950c36c0ec67ba;hp=4bf4cebb69ece2947eb1deccf0dfa9cfda20f266;hpb=58cf11569acb270995d2de924dda03ef526647e2;p=spline3.git

diff --git a/src/Comparisons.hs b/src/Comparisons.hs
index 4bf4ceb..3bf4e24 100644
--- a/src/Comparisons.hs
+++ b/src/Comparisons.hs
@@ -1,13 +1,33 @@
 -- | Functions for comparing 'Double' values.
-module Comparisons
+module Comparisons (
+  (~=),
+  (~~=),
+  almost_equals,
+  kinda_equals,
+  nearly_equals,
+  nearly_ge,
+  non_very_positive_entries,
+  very_positive,
+  )
 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
@@ -18,6 +38,20 @@ 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