+
+
+-- | Retrieve the rows of a matrix as a column matrix. If the given
+-- matrix is m-by-n, the result would be an m-by-1 column whose
+-- entries are 1-by-n row matrices.
+--
+-- Examples:
+--
+-- >>> let m = fromList [[1,2],[3,4]] :: Mat2 Int
+-- >>> (rows2 m) !!! (0,0)
+-- ((1,2))
+-- >>> (rows2 m) !!! (1,0)
+-- ((3,4))
+--
+rows2 :: (Arity m, Arity n)
+ => Mat m n a
+ -> Col m (Row n a)
+rows2 (Mat rows) =
+ Mat $ V.map (mk1. Mat . mk1) rows
+
+
+
+-- | Sum the elements of a matrix.
+--
+-- Examples:
+--
+-- >>> let m = fromList [[1,-1],[3,4]] :: Mat2 Int
+-- >>> element_sum2 m
+-- 7
+--
+element_sum2 :: (Arity m, Arity n, Additive.C a) => Mat m n a -> a
+element_sum2 = foldl2 (+) zero