diff --git a/src/Data/NumIdr/Matrix.idr b/src/Data/NumIdr/Matrix.idr
index 4acf004..8e89120 100644
--- a/src/Data/NumIdr/Matrix.idr
+++ b/src/Data/NumIdr/Matrix.idr
@@ -2,7 +2,7 @@ module Data.NumIdr.Matrix
 
 import Data.List
 import Data.Vect
-import Data.Bool.Xor
+import Data.Permutation
 import Data.NumIdr.Multiply
 import public Data.NumIdr.Array
 import Data.NumIdr.Vector
@@ -61,6 +61,11 @@ fromDiag ds o = fromFunction [m,n] (\[i,j] => maybe o (`index` ds) $ i `eq` j)
     eq (FS _) FZ = Nothing
 
 
+export
+permutationMatrix : {n : _} -> Num a => Permutation n -> Matrix' n a
+permutationMatrix p = permuteInAxis 0 p (repeatDiag 1 0)
+
+
 ||| Construct the matrix that scales a vector by the given value.
 export
 scaling : {n : _} -> Num a => a -> Matrix' n a
@@ -117,6 +122,27 @@ minor : Fin (S m) -> Fin (S n) -> Matrix (S m) (S n) a -> Matrix m n a
 minor i j mat = believe_me $ mat!!..[Filter (/=i), Filter (/=j)]
 
 
+filterInd : Num a => (Nat -> Nat -> Bool) -> Matrix m n a -> Matrix m n a
+filterInd p mat with (viewShape mat)
+  _ | Shape [m,n] = fromFunctionNB [m,n] (\[i,j] => if p i j then mat!#[i,j] else 0)
+
+export
+upperTriangle : Num a => Matrix m n a -> Matrix m n a
+upperTriangle = filterInd (<=)
+
+export
+lowerTriangle : Num a => Matrix m n a -> Matrix m n a
+lowerTriangle = filterInd (>=)
+
+export
+upperTriangleStrict : Num a => Matrix m n a -> Matrix m n a
+upperTriangleStrict = filterInd (<)
+
+export
+lowerTriangleStrict : Num a => Matrix m n a -> Matrix m n a
+lowerTriangleStrict = filterInd (>)
+
+
 --------------------------------------------------------------------------------
 -- Basic operations
 --------------------------------------------------------------------------------
@@ -141,6 +167,23 @@ hstack : {m : _} -> Vect n (Vector m a) -> Matrix m n a
 hstack = stack 1
 
 
+export
+swapRows : (i,j : Fin m) -> Matrix m n a -> Matrix m n a
+swapRows = swapInAxis 0
+
+export
+swapColumns : (i,j : Fin n) -> Matrix m n a -> Matrix m n a
+swapColumns = swapInAxis 1
+
+export
+permuteRows : Permutation m -> Matrix m n a -> Matrix m n a
+permuteRows = permuteInAxis 0
+
+export
+permuteColumns : Permutation n -> Matrix m n a -> Matrix m n a
+permuteColumns = permuteInAxis 1
+
+
 ||| Calculate the outer product of two vectors as a matrix.
 export
 outer : Num a => Vector m a -> Vector n a -> Matrix m n a
@@ -181,14 +224,29 @@ export
 
 
 -- LU Decomposition
-public export
+export
 record DecompLU {0 n,a : _} (mat : Matrix' n a) where
   constructor MkLU
-  lower, upper : Matrix' n a
+  lu : Matrix' n a
 
-export
-Show a => Show (DecompLU {a} mat) where
-  showPrec p (MkLU l u) = showCon p "MkLU" $ showArg l ++ showArg u
+
+namespace DecompLU
+  export
+  lower : Num a => DecompLU {n,a} mat -> Matrix' n a
+  lower (MkLU lu) with (viewShape lu)
+    _ | Shape [n,n] = lowerTriangleStrict lu + identity
+
+  export %inline
+  (.lower) : Num a => DecompLU {n,a} mat -> Matrix' n a
+  (.lower) = lower
+
+  export
+  upper : Num a => DecompLU {n,a} mat -> Matrix' n a
+  upper (MkLU lu) = upperTriangle lu
+
+  export %inline
+  (.upper) : Num a => DecompLU {n,a} mat -> Matrix' n a
+  (.upper) = upper
 
 
 iterateN : (n : Nat) -> (Fin n -> a -> a) -> a -> a
@@ -196,45 +254,75 @@ iterateN 0 f x = x
 iterateN 1 f x = f FZ x
 iterateN (S n@(S _)) f x = iterateN n (f . FS) $ f FZ x
 
+
+gaussStep : (Eq a, Neg a, Fractional a) => Fin n -> Matrix' n a -> Matrix' n a
+gaussStep {n} i lu with (viewShape lu)
+  _ | Shape [n,n] =
+    if all (==0) $ getColumn i lu then lu else
+      let diag = lu!![i,i]
+          coeffs = map (/diag) $ lu!!..[StartBound (FS i), One i]
+          lu' = indexSetRange [StartBound (FS i), One i]
+                  coeffs lu
+          pivot = lu!!..[One i, StartBound (FS i)]
+          offsets = negate $ outer coeffs pivot
+      in  indexUpdateRange [StartBound (FS i), StartBound (FS i)] (+offsets) lu'
+
 export
-decompLU : Neg a => Fractional a => (mat : Matrix' n a) -> DecompLU mat
+decompLU : (Eq a, Neg a, Fractional a) => (mat : Matrix' n a) -> DecompLU mat
 decompLU {n} mat with (viewShape mat)
-  _ | Shape [n,n] = iterateN n doolittle (MkLU identity mat)
-  where
-    doolittle : Fin n -> DecompLU mat -> DecompLU mat
-    doolittle i (MkLU l u) =
-      let v = rewrite rangeLen (S i') n in fromFunctionNB [minus n (S i')]
-                (\[x] => u!#[S i' + x,i'] / u!#[i',i'])
-          low = indexSetRange [StartBound (FS i), One i] (-v) identity
-      in MkLU (indexSetRange [StartBound (FS i), One i] v l) (low *. u)
-      where i' : Nat
-            i' = cast i
+  _ | Shape [n,n] = MkLU $ iterateN n gaussStep mat
 
 
 -- LUP Decomposition
 public export
 record DecompLUP {0 n,a : _} (mat : Matrix' n a) where
   constructor MkLUP
-  lower, upper, permute : Matrix' n a
-  swaps : Nat
+  lu : Matrix' n a
+  p : Permutation n
+  sw : Nat
+
+namespace DecompLUP
+  export
+  lower : Num a => DecompLUP {n,a} mat -> Matrix' n a
+  lower (MkLUP lu p sw) with (viewShape lu)
+    _ | Shape [n,n] = lowerTriangleStrict lu + identity
+
+  export %inline
+  (.lower) : Num a => DecompLUP {n,a} mat -> Matrix' n a
+  (.lower) = lower
+
+  export
+  upper : Num a => DecompLUP {n,a} mat -> Matrix' n a
+  upper (MkLUP lu p sw) = upperTriangle lu
+
+  export %inline
+  (.upper) : Num a => DecompLUP {n,a} mat -> Matrix' n a
+  (.upper) = upper
+
+  export
+  permute : DecompLUP {n} mat -> Permutation n
+  permute (MkLUP lu p sw) = p
+
+  export %inline
+  (.permute) : DecompLUP {n} mat -> Permutation n
+  (.permute) = permute
+
+  export
+  numSwaps : DecompLUP {n} mat -> Nat
+  numSwaps (MkLUP lu p sw) = sw
 
 export
-Show a => Show (DecompLUP {a} mat) where
-  showPrec p (MkLUP l u pr b) = showCon p "MkLUP" $
-    showArg l ++ showArg u ++ showArg pr ++ showArg b
+fromLU : DecompLU mat -> DecompLUP mat
+fromLU (MkLU lu) = MkLUP lu identity 0
+
 
 export
-fromLU : Num a => DecompLU {n,a} mat -> DecompLUP mat
-fromLU {n} (MkLU l u) with (viewShape l)
-  _ | Shape [n,n] = MkLUP l u identity 0
-
-export
-decompLUP : Ord a => Abs a => Neg a => Fractional a =>
+decompLUP : (Ord a, Abs a, Neg a, Fractional a) =>
             (mat : Matrix' n a) -> DecompLUP mat
 decompLUP {n} mat with (viewShape mat)
-  decompLUP {n=0} mat | Shape [0,0] = MkLUP mat mat mat 0
+  decompLUP {n=0} mat | Shape [0,0] = MkLUP mat identity 0
   decompLUP {n=S n} mat | Shape [S n,S n] =
-    iterateN (S n) doolittle (MkLUP identity mat identity 0)
+    iterateN (S n) gaussStepSwap (MkLUP mat identity 0)
   where
     maxIndex : (s,a) -> List (s,a) -> (s,a)
     maxIndex x [] = x
@@ -243,29 +331,13 @@ decompLUP {n} mat with (viewShape mat)
       if abs b < abs d then assert_total $ maxIndex x ((c,d)::xs)
                        else assert_total $ maxIndex x ((a,b)::xs)
 
-    doolittle : Fin (S n) -> DecompLUP mat -> DecompLUP mat
-    doolittle i (MkLUP l u p sw) =
-      let (maxi, maxv) = mapFst ((+i') . head)
-                           (maxIndex ([0],0) $ enumerateNB $
-                           u !!.. [StartBound (weaken i), One i])
-          u' = if maxi == i' then u
-               else fromFunctionNB _ (\[x,y] =>
-                 if x==i' then u!#[maxi,y]
-                 else if x==maxi then u!#[i',y]
-                 else u!#[x,y])
-          p' = if maxi == i' then p
-               else fromFunctionNB _ (\[x,y] =>
-                 if x==i' then p!#[maxi,y]
-                 else if x==maxi then p!#[i',y]
-                 else p!#[x,y])
-          v = rewrite rangeLen (S i') (S n) in fromFunctionNB [minus n i']
-                (\[x] => u'!#[S i' + x,i'] / u'!#[i',i'])
-          low = indexSetRange [StartBound (FS i), One i] (-v) identity
-      in if maxv == 0 then MkLUP l u p sw else
-            MkLUP (indexSetRange [StartBound (FS i), One i] v l)
-              (low *. u') p' (if maxi==i' then S sw else sw)
-      where i' : Nat
-            i' = cast i
+    gaussStepSwap : Fin (S n) -> DecompLUP mat -> DecompLUP mat
+    gaussStepSwap i (MkLUP lu p sw) =
+      let (maxi, maxv) = mapFst head
+                           (maxIndex ([0],0) $ enumerate $
+                           indexSetRange [EndBound (weaken i)] 0 $ getColumn i lu)
+      in  if maxi == i then MkLUP (gaussStep i lu) p sw
+          else MkLUP (gaussStep i $ swapRows maxi i lu) (appendSwap maxi i p) (S sw)
 
 
 --------------------------------------------------------------------------------
@@ -274,12 +346,16 @@ decompLUP {n} mat with (viewShape mat)
 
 
 export
-det : Ord a => Abs a => Neg a => Fractional a =>
-      Matrix' n a -> a
+detWithLUP : (Ord a, Abs a, Neg a, Fractional a) =>
+            (mat : Matrix' n a) -> DecompLUP mat -> a
+detWithLUP {n} mat lup =
+  (if numSwaps lup `mod` 2 == 0 then 1 else -1)
+    * product (diagonal lup.lower) * product (diagonal lup.upper)
+
+export
+det : (Ord a, Abs a, Neg a, Fractional a) => Matrix' n a -> a
 det {n} mat with (viewShape mat)
   det {n=0} mat | Shape [0,0] = 1
   det {n=1} mat | Shape [1,1] = mat!![0,0]
   det {n=2} mat | Shape [2,2] = let [a,b,c,d] = elements mat in a*d - b*c
-  _ | Shape [n,n] = let MkLUP l u p sw = decompLUP mat
-                    in (if sw `mod` 2 == 0 then 1 else -1)
-                          * product (diagonal l) * product (diagonal u)
+  _ | Shape [n,n] = detWithLUP mat (decompLUP mat)
diff --git a/src/Data/Permutation.idr b/src/Data/Permutation.idr
index cb15fcd..4f3a48b 100644
--- a/src/Data/Permutation.idr
+++ b/src/Data/Permutation.idr
@@ -15,6 +15,10 @@ export
 swap : (i,j : Fin n) -> Permutation n
 swap x y = MkPerm [(x,y)]
 
+export
+swaps : List (Fin n, Fin n) -> Permutation n
+swaps = MkPerm
+
 export
 appendSwap : (i,j : Fin n) -> Permutation n -> Permutation n
 appendSwap i j (MkPerm a) = MkPerm ((i,j)::a)
@@ -51,6 +55,12 @@ export
 permuteValues : Permutation n -> Nat -> Nat
 permuteValues p = foldMap @{%search} @{mon} (\(i,j) => swapValues i j) p.swaps
 
+
+
+export
+Show (Permutation n) where
+  showPrec p (MkPerm a) = showCon p "swaps" $ showArg a
+
 export
 Mult (Permutation n) (Permutation n) (Permutation n) where
   MkPerm a *. MkPerm b = MkPerm (a ++ b)