2 files changed, 15 insertions, 5 deletions

diff --git a/lib/Data/Packed/Internal/Matrix.hs b/lib/Data/Packed/Internal/Matrix.hs
index 77906dc..605a6f3 100644
--- a/lib/Data/Packed/Internal/Matrix.hs
+++ b/lib/Data/Packed/Internal/Matrix.hs
@@ -48,12 +48,14 @@ import Data.List(transpose)
 - we could carry both the matrix and its (lazily computed) transpose.
   This may save some transpositions, but it is necessary to keep track of the
   data which is actually computed to be used by functions like the matrix product
-  which admit both orders. Therefore, maybe it is better to have something like
-  viewC and viewF, which may actually perform a transpose if required.
+  which admit both orders.
 
 - but if we need the transposed data and it is not in the structure, we must make
-  sure that we touch the same foreignptr that is used in the computation. Access
-  to such pointer cannot be made by creating a new vector.
+  sure that we touch the same foreignptr that is used in the computation.
+
+- a reasonable solution is using two constructors for a matrix. Transposition just
+  "flips" the constructor. Actual data transposition is not done if followed by a
+  matrix product or another transpose.
 
 -}
 
@@ -66,7 +68,7 @@ data Matrix t = MC { rows :: Int, cols :: Int, cdat :: Vector t, fdat :: Vector
 -- MC: preferred by C, fdat may require a transposition
 -- MF: preferred by LAPACK, cdat may require a transposition
 
--- | matrix transpose
+-- | Matrix transpose.
 trans :: Matrix t -> Matrix t
 trans MC {rows = r, cols = c, cdat = d, fdat = dt } = MF {rows = c, cols = r, fdat = d, cdat = dt }
 trans MF {rows = r, cols = c, fdat = d, cdat = dt } = MC {rows = c, cols = r, cdat = d, fdat = dt }
diff --git a/lib/Data/Packed/Matrix.hs b/lib/Data/Packed/Matrix.hs
index e94d038..a705975 100644
--- a/lib/Data/Packed/Matrix.hs
+++ b/lib/Data/Packed/Matrix.hs
@@ -193,6 +193,14 @@ dsp' sep as = unlines . map unwords' $ transpose mtp where
     pad n str = replicate (n - length str) ' ' ++ str
     unwords' = concat . intersperse sep
 
+{- | Creates a string from a matrix given a separator and a function to show each entry. Using
+this function the user can easily define any desired display function:
+
+@import Text.Printf(printf)@
+
+@disp = putStrLn . format \"  \" (printf \"%.2f\")@
+
+-}
 format :: (Field t) => String -> (t -> String) -> Matrix t -> String
 format sep f m = dsp' sep . map (map f) . toLists $ m