Require a matrix to be nonempty if we're going to QR factorize it.

diff --git a/src/Linear/QR.hs b/src/Linear/QR.hs
index 8d9ea42a1e19bd880ffb9211238e53ba3d7b8c5b..4c1c56446f836c348b1b7e65ad138fb650dd9ed3 100644 (file)
--- a/src/Linear/QR.hs
+++ b/src/Linear/QR.hs
@@ -140,7 +140,8 @@ givens_rotator i j xi xj =
 --   True
 --
 qr :: forall m n a. (Arity m, Arity n, Eq a, Algebraic.C a, Ring.C a)
-   => Mat m n a -> (Mat m m a, Mat m n a)
+   => Mat (S m) (S n) a
+   -> (Mat (S m) (S m) a, Mat (S m) (S n) a)
 qr matrix =
   ifoldl col_function initial_qr columns
   where
@@ -162,7 +163,7 @@ qr matrix =
       | otherwise = (q*rotator, (transpose rotator)*r)
           where
             y = r !!! (idx, col_idx)
-            rotator :: Mat m m a
+            rotator :: Mat (S m) (S m) a
             rotator = givens_rotator col_idx idx (r !!! (col_idx, col_idx)) y