From d8dc884aa9b16c7bbd88c4c107ddd684a339a191 Mon Sep 17 00:00:00 2001
From: Michael Orlitzky <michael@orlitzky.com>
Date: Sun, 2 Feb 2014 18:46:05 -0500
Subject: [PATCH] Switch Linear.Vector to the numeric prelude and add the
 element_sum function to it. Use Linear.Vector.element_sum in Linear.Matrix.

---
 src/Linear/Matrix.hs | 15 ++++-----------
 src/Linear/Vector.hs | 43 +++++++++++++++++++++++++++++++++----------
 2 files changed, 37 insertions(+), 21 deletions(-)

diff --git a/src/Linear/Matrix.hs b/src/Linear/Matrix.hs
index 66b22f9..69a74b5 100644
--- a/src/Linear/Matrix.hs
+++ b/src/Linear/Matrix.hs
@@ -35,7 +35,6 @@ import Data.Vector.Fixed (
   )
 import qualified Data.Vector.Fixed as V (
   and,
-  foldl,
   fromList,
   head,
   length,
@@ -45,7 +44,6 @@ import qualified Data.Vector.Fixed as V (
   toList,
   zipWith
   )
-import Data.Vector.Fixed.Boxed (Vec)
 import Data.Vector.Fixed.Cont (Arity, arity)
 import Linear.Vector
 import Normed
@@ -430,8 +428,8 @@ instance (Algebraic.C a,
           ToRational.C a,
           Arity m)
          => Normed (Mat (S m) N1 a) where
-  -- | Generic p-norms. The usual norm in R^n is (norm_p 2). We treat
-  --   all matrices as big vectors.
+  -- | Generic p-norms for vectors in R^n that are represented as nx1
+  --   matrices.
   --
   --   Examples:
   --
@@ -475,15 +473,10 @@ instance (Algebraic.C a,
 --
 frobenius_norm :: (Algebraic.C a, Ring.C a) => Mat m n a -> a
 frobenius_norm (Mat rows) =
-  sqrt $ vsum $ V.map row_sum rows
+  sqrt $ element_sum $ V.map row_sum rows
   where
-    -- | The \"sum\" function defined in fixed-vector requires a 'Num'
-    --   constraint whereas we want to use the classes from
-    --   numeric-prelude.
-    vsum = V.foldl (+) (fromInteger 0)
-
     -- | Square and add up the entries of a row.
-    row_sum = vsum . V.map (^2)
+    row_sum = element_sum . V.map (^2)
 
 
 -- Vector helpers. We want it to be easy to create low-dimension
diff --git a/src/Linear/Vector.hs b/src/Linear/Vector.hs
index e4f6225..9d43bfa 100644
--- a/src/Linear/Vector.hs
+++ b/src/Linear/Vector.hs
@@ -1,31 +1,40 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 
-module Linear.Vector
+module Linear.Vector (
+  module Data.Vector.Fixed.Boxed,
+  Vec1,
+  (!?),
+  delete,
+  element_sum )
 where
 
+import qualified Algebra.Additive as Additive ( C )
+import qualified Algebra.Ring as Ring ( C )
 import Data.Vector.Fixed (
   Dim,
   N1,
-  N4,
-  N5,
   S,
   Vector(..),
   fromList,
-  toList,
-  )
+  toList )
 import qualified Data.Vector.Fixed as V (
   (!),
-  length,
-  )
-import Data.Vector.Fixed.Boxed
+  foldl,
+  length )
+import Data.Vector.Fixed.Boxed (
+  Vec,
+  Vec2,
+  Vec3,
+  Vec4,
+  Vec5 )
+import NumericPrelude hiding ( abs )
 
 type Vec1 = Vec N1
-type Vec4 = Vec N4
-type Vec5 = Vec N5
 
 
 
@@ -66,3 +75,17 @@ delete v1 idx =
   where
     (lhalf, rhalf) = splitAt idx (toList v1)
     rhalf' = tail rhalf
+
+
+-- | We provide our own sum because V.sum relies on a Num instance
+--   from the Prelude that we don't have.
+--
+--   Examples:
+--
+--   >>> import Data.Vector.Fixed (mk3)
+--   >>> let b = mk3 1 2 3 :: Vec3 Int
+--   >>> element_sum b
+--   6
+--
+element_sum :: (Additive.C a, Ring.C a, Vector v a) => v a -> a
+element_sum = V.foldl (+) (fromInteger 0)
-- 
2.44.2