[#118] Add test to divModE

Bodigrim · Aug 13, 2018 · 76d2415 · 76d2415
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diff --git a/Math/NumberTheory/EisensteinIntegers.hs b/Math/NumberTheory/EisensteinIntegers.hs
@@ -100,38 +100,38 @@ divModE alfa beta | norm rho1 < norm rho2 = (gamma1, rho1)
 
     -- First step of assignments performed in the Division Algorithm from
     -- Theorem 4.1.1.
-    alfa'                = eisensteinToComplex alfa
-    beta'                = eisensteinToComplex beta
-    a1 C.:+ b1           = alfa' / beta'
-    a2 C.:+ b2           = alfa' / beta' - eisensteinToComplex ω
+    alfa'              = eisensteinToComplex alfa
+    beta'              = eisensteinToComplex beta
+    a1 C.:+ b1         = alfa' / beta'
+    a2 C.:+ b2         = (alfa' / beta') - eisensteinToComplex ω
 
     -- @round@s a @Double@ and returns that as another @Double@.
-    dToIToD              :: Double -> Double
-    dToIToD              = (fromIntegral :: Integer -> Double) . round
+    dToIToD            :: Double -> Double
+    dToIToD            = (fromIntegral :: Integer -> Double) . round
 
     -- Second step of assignments performed in the Division Algorithm from
     -- Theorem 4.1.1.
-    properFraction' :: Double -> (Integer, Double)
-    properFraction' = properFraction
-    rho'                 :: Double -> Double -> C.Complex Double
-    rho' a' b'           = (snd $ properFraction' a') C.:+ (b' - sqrt3 * dToIToD (b' / sqrt3))
-    rho1'               = rho' a1 b1
-    rho2'               = rho' a2 b2
+    properFraction'    :: Double -> (Integer, Double)
+    properFraction'    = properFraction
+    rho'               :: Double -> Double -> C.Complex Double
+    rho' a' b'         = (snd $ properFraction' a') C.:+ (b' - sqrt3 * dToIToD (b' / sqrt3))
+    rho1'              = rho' a1 b1
+    rho2'              = rho' a2 b2
 
     -- Converts a complex number in the form @a + bι@, where @a, b@ are
     -- @Double@s, into an @EisensteinInteger@ in the form @α + βω@, where
     -- @α, β@ are @Integer@s.
-    toEisen              :: C.Complex Double -> EisensteinInteger
-    toEisen (x C.:+ y)   = round (x + y / sqrt3) :+ round (y * 2 / sqrt3)
+    toEisen            :: C.Complex Double -> EisensteinInteger
+    toEisen (x C.:+ y) = round (x + y / sqrt3) :+ round (y * 2 / sqrt3)
 
-    -- Third step of assignments performed in the Division Alrgorithm from
+    -- Third step of assignments performed in the Division Algorithm from
     -- Theorem 4.1.1.
-    rho1                 = toEisen $ beta' * rho1'
-    b1sqrt3'             = round $ b1 / sqrt3
-    gamma1               = ((round a1) + b1sqrt3') :+ (2 * b1sqrt3')
-    rho2                 = toEisen $ beta' * rho2'
-    b2sqrt3'             = round $ b2 / sqrt3
-    gamma2               = ((round a2) + b2sqrt3') :+ (1 + 2 * b2sqrt3')
+    rho1               = toEisen $ beta' * rho1'
+    b1sqrt3'           = round $ b1 / sqrt3
+    gamma1             = ((round a1) + b1sqrt3') :+ (2 * b1sqrt3')
+    rho2               = toEisen $ beta' * rho2'
+    b2sqrt3'           = round $ b2 / sqrt3
+    gamma2             = ((round a2) + b2sqrt3') :+ (1 + 2 * b2sqrt3')
 
 
 -- | Eisenstein integer division, truncating toward negative infinity.

diff --git a/test-suite/Math/NumberTheory/EisensteinIntegersTests.hs b/test-suite/Math/NumberTheory/EisensteinIntegersTests.hs
@@ -38,9 +38,14 @@ absProperty z = isOrigin || (inFirstSextant && isAssociate)
     inFirstSextant = x' > y' && y' >= 0
     isAssociate = z' `elem` map (\e -> z * (1 E.:+ 1) ^ e) [0 .. 5]
 
+-- | Verify that `divModE` produces the right quotient and remainder.
+divModProperty1 :: E.EisensteinInteger -> E.EisensteinInteger -> Bool
+divModProperty1 x y = (y == 0) || (x `E.divE` y) * y + (x `E.modE` y) == x
+
 testSuite :: TestTree
 testSuite = testGroup "EisensteinIntegers" $
   [ testSmallAndQuick "forall z . z == signum z * abs z" signumAbsProperty
   , testSmallAndQuick "abs z always returns an @EisensteinInteger@ in the\
                       \ first sextant of the complex plane" absProperty
+  , testSmallAndQuick "divModE works properly" divModProperty1
   ]