Fix the type of zip2 to be more general.

[numerical-analysis.git] / src / Linear / Matrix.hs

diff --git a/src/Linear/Matrix.hs b/src/Linear/Matrix.hs
index 2422eefcb7e269de1e5104ddb1c559b4c5c73e34..82665578cf037def7c04ef223a8b6e350ad9232f 100644 (file)
--- a/src/Linear/Matrix.hs
+++ b/src/Linear/Matrix.hs
@@ -579,11 +579,12 @@ instance (Ring.C a, Arity m, Arity n) => Module.C a (Mat m n a) where
   x *> (Mat rows) = Mat $ V.map (V.map (NP.* x)) rows
 
 
-instance (Algebraic.C a,
+instance (Absolute.C a,
+          Algebraic.C a,
           ToRational.C a,
           Arity m)
-         => Normed (Mat (S m) N1 a) where
-  -- | Generic p-norms for vectors in R^n that are represented as nx1
+         => Normed (Col (S m) a) where
+  -- | Generic p-norms for vectors in R^n that are represented as n-by-1
   --   matrices.
   --
   --   Examples:
@@ -594,8 +595,12 @@ instance (Algebraic.C a,
   --   >>> norm_p 2 v1
   --   5.0
   --
+  --   >>> let v1 = vec2d (-1,1) :: Col2 Double
+  --   >>> norm_p 1 v1 :: Double
+  --   2.0
+  --
   norm_p p (Mat rows) =
-    (root p') $ sum [fromRational' (toRational x)^p' | x <- xs]
+    (root p') $ sum [fromRational' (toRational $ abs x)^p' | x <- xs]
     where
       p' = toInteger p
       xs = concat $ V.toList $ V.map V.toList rows
@@ -851,7 +856,7 @@ trace matrix =
 --   >>> zip2 m1 m2
 --   (((1,1),(2,1)),((3,1),(4,1)))
 --
-zip2 :: (Arity m, Arity n) => Mat m n a -> Mat m n a -> Mat m n (a,a)
+zip2 :: (Arity m, Arity n) => Mat m n a -> Mat m n b -> Mat m n (a,b)
 zip2 m1 m2 =
   construct lambda
   where