diff --git a/src/Data/NumIdr/Matrix.idr b/src/Data/NumIdr/Matrix.idr
index 37352f7..acc012d 100644
--- a/src/Data/NumIdr/Matrix.idr
+++ b/src/Data/NumIdr/Matrix.idr
@@ -394,7 +394,7 @@ decompLUP {m,n} mat with (viewShape mat)
   decompLUP {m=0,n} mat | Shape [0,n] = MkLUP mat identity 0
   decompLUP {m=S m,n=0} mat | Shape [S m,0] = MkLUP mat identity 0
   decompLUP {m=S m,n=S n} mat | Shape [S m,S n] =
-    iterateN (minimum (S m) (S n)) gaussStepSwap (MkLUP mat identity 0)
+    iterateN (S $ minimum m n) gaussStepSwap (MkLUP mat identity 0)
   where
     maxIndex : (s,a) -> List (s,a) -> (s,a)
     maxIndex x [] = x
@@ -403,15 +403,14 @@ decompLUP {m,n} mat with (viewShape mat)
       if abscmp b d == LT then assert_total $ maxIndex x ((c,d)::xs)
                           else assert_total $ maxIndex x ((a,b)::xs)
 
-    gaussStepSwap : Fin (minimum (S m) (S n)) -> DecompLUP mat -> DecompLUP mat
+    gaussStepSwap : Fin (S $ minimum m n) -> DecompLUP mat -> DecompLUP mat
     gaussStepSwap i (MkLUP lu p sw) =
       let ir = minWeakenLeft {n=S n} i
           ic = minWeakenRight {m=S m} i
-          (maxi, maxv) = mapFst head
-                           (maxIndex ([0],0) $ enumerate $
+          maxi = head $ fst (maxIndex ([0],0) $ drop (cast i) $ enumerate $
                            indexSetRange [EndBound (weaken ir)] 0 $ getColumn ic lu)
       in  if maxi == ir then MkLUP (gaussStep i lu) p sw
-          else MkLUP (gaussStep i $ swapRows maxi ir lu) (appendSwap maxi ir p) (S sw)
+          else MkLUP (gaussStep i $ swapRows ir maxi lu) (appendSwap maxi ir p) (S sw)
 
 
 --------------------------------------------------------------------------------
@@ -439,13 +438,9 @@ det {n} mat with (viewShape mat)
 --------------------------------------------------------------------------------
 
 
-export
-solveLowerTri : Field a => Matrix' n a -> Vector n a -> Maybe (Vector n a)
-solveLowerTri {n} mat b with (viewShape b)
-  _ | Shape [n] =
-    if all (/=0) (diagonal mat)
-    then Just $ vector $ reverse $ construct $ reverse $ toVect b
-    else Nothing
+solveLowerTri' : Field a => Matrix' n a -> Vector n a -> Vector n a
+solveLowerTri' {n} mat b with (viewShape b)
+  _ | Shape [n] = vector $ reverse $ construct $ reverse $ toVect b
   where
     construct : {i : _} -> Vect i a -> Vect i a
     construct [] = []
@@ -455,13 +450,10 @@ solveLowerTri {n} mat b with (viewShape b)
       in (b - sum (zipWith (*) xs (reverse $ toVect $ believe_me $
                   mat !!.. [One i', EndBound (weaken i')]))) / mat!#[i,i] :: xs
 
-export
-solveUpperTri : Field a => Matrix' n a -> Vector n a -> Maybe (Vector n a)
-solveUpperTri {n} mat b with (viewShape b)
-  _ | Shape [n] =
-    if all (/=0) (diagonal mat)
-    then Just $ vector $ construct Z $ toVect b
-    else Nothing
+
+solveUpperTri' : Field a => Matrix' n a -> Vector n a -> Vector n a
+solveUpperTri' {n} mat b with (viewShape b)
+  _ | Shape [n] = vector $ construct Z $ toVect b
   where
     construct : Nat -> Vect i a -> Vect i a
     construct _ [] = []
@@ -471,6 +463,26 @@ solveUpperTri {n} mat b with (viewShape b)
       in (b - sum (zipWith (*) xs (toVect $ believe_me $
                   mat !!.. [One i', StartBound (FS i')]))) / mat!#[i,i] :: xs
 
+
+export
+solveLowerTri : Field a => Matrix' n a -> Vector n a -> Maybe (Vector n a)
+solveLowerTri mat b = if all (/=0) (diagonal mat)
+                      then Just $ solveLowerTri' mat b
+                      else Nothing
+
+export
+solveUpperTri : Field a => Matrix' n a -> Vector n a -> Maybe (Vector n a)
+solveUpperTri mat b = if all (/=0) (diagonal mat)
+                      then Just $ solveUpperTri' mat b
+                      else Nothing
+
+
+solveWithLUP' : Field a => (mat : Matrix' n a) -> DecompLUP mat ->
+                Vector n a -> Vector n a
+solveWithLUP' mat lup b =
+  let b' = permuteCoords (inverse lup.permute) b
+  in solveUpperTri' lup.upper' $ solveLowerTri' lup.lower' b'
+
 export
 solveWithLUP : Field a => (mat : Matrix' n a) -> DecompLUP mat ->
                 Vector n a -> Maybe (Vector n a)
@@ -478,6 +490,22 @@ solveWithLUP mat lup b =
   let b' = permuteCoords (inverse lup.permute) b
   in solveLowerTri lup.lower' b' >>= solveUpperTri lup.upper'
 
+
 export
 solve : FieldCmp a => Matrix' n a -> Vector n a -> Maybe (Vector n a)
 solve mat = solveWithLUP mat (decompLUP mat)
+
+
+export
+tryInverse : FieldCmp a => Matrix' n a -> Maybe (Matrix' n a)
+tryInverse {n} mat with (viewShape mat)
+  _ | Shape [n,n] =
+    let lup = decompLUP mat
+    in map hstack $ traverse (solveWithLUP mat lup) $ map basis range
+
+
+export
+{n : _} -> FieldCmp a => MultGroup (Matrix' n a) where
+  inverse mat = let lup = decompLUP mat in
+        hstack $ map (solveWithLUP' mat lup . basis) range
+