X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=src%2FTwoTuple.hs;h=3950fee9afeabd5bfb8d884ca6543c4689873c24;hb=74e79199dcfec0639133ae9990dc33a2c5a095f0;hp=daeb6e41f8cdbbbe43e11139236dbc88f5955c18;hpb=ff83c063ad5cdb1bf9476678a010aa0cfb782a8f;p=numerical-analysis.git

diff --git a/src/TwoTuple.hs b/src/TwoTuple.hs
index daeb6e4..3950fee 100644
--- a/src/TwoTuple.hs
+++ b/src/TwoTuple.hs
@@ -1,5 +1,7 @@
 -- | Implement ordered pairs all over again for fun (and to make sure
---   that we can manipulate them algebraically).
+--   that we can manipulate them algebraically). Also require (as
+--   opposed to the built-in ordered pairs) that the elements have
+--   matching types.
 --
 module TwoTuple
 where
@@ -8,7 +10,10 @@ import Vector
 
 
 data TwoTuple a = TwoTuple a a
-  deriving (Eq, Show)
+  deriving (Eq)
+
+instance (Show a) => Show (TwoTuple a) where
+  show (TwoTuple x y) = "(" ++ (show x) ++ ", " ++ (show y) ++ ")"
 
 instance Functor TwoTuple where
   f `fmap` (TwoTuple x1 y1) = TwoTuple (f x1) (f y1)
@@ -16,7 +21,14 @@ instance Functor TwoTuple where
 instance (RealFloat a) => Vector (TwoTuple a) where
   -- The standard Euclidean 2-norm. We need RealFloat for the square
   -- root.
-  norm (TwoTuple x1 y1) = fromRational $ toRational (sqrt(x1^2 + y1^2))
+  norm_2 (TwoTuple x y) = fromRational $ toRational (sqrt(x^2 + y^2))
+
+  -- The infinity norm, i.e. the maximum entry.
+  norm_infty (TwoTuple x y) =
+    fromRational $ max absx absy
+    where
+      absx = abs (toRational x)
+      absy = abs (toRational y)
 
 -- | It's not correct to use Num here, but I really don't want to have
 --   to define my own addition and subtraction.