2 files changed, 44 insertions, 8 deletions

diff --git a/lib/Numeric/ContainerBoot.hs b/lib/Numeric/ContainerBoot.hs
index d9f0d78..250d4c5 100644
--- a/lib/Numeric/ContainerBoot.hs
+++ b/lib/Numeric/ContainerBoot.hs
@@ -121,15 +121,8 @@ class (Complexable c, Fractional e, Element e) => Container c e where
     sumElements :: c e -> e
     -- | the product of elements (faster than using @fold@)
     prodElements :: c e -> e
-    -- | a more efficient implementation of @cmap (\x -> if x>0 then 1 else 0)@
+    -- | a more efficient implementation of @cmap (\\x -> if x>0 then 1 else 0)@
     step :: RealElement e => c e -> c e
-    -- | find index of elements which satisfy a predicate
-    find :: (e -> Bool) -> c e -> [IndexOf c]
-    -- | create a structure from an association list
-    assoc :: IndexOf c        -- ^ size
-          -> e                -- ^ default value
-          -> [(IndexOf c, e)] -- ^ association list
-          -> c e              -- ^ result
 
     -- | element by element @case compare a b of LT -> l, EQ -> e, GT -> g@
     cond :: RealElement e 
@@ -140,6 +133,21 @@ class (Complexable c, Fractional e, Element e) => Container c e where
          -> c e -- ^ g
          -> c e -- ^ result
 
+    -- | find index of elements which satisfy a predicate
+    find :: (e -> Bool) -> c e -> [IndexOf c]
+
+    -- | create a structure from an association list
+    assoc :: IndexOf c        -- ^ size
+          -> e                -- ^ default value
+          -> [(IndexOf c, e)] -- ^ association list
+          -> c e              -- ^ result
+
+    -- | modify a structure using an update function
+    accum :: c e              -- ^ initial structure
+          -> (e -> e -> e)    -- ^ update function
+          -> [(IndexOf c, e)] -- ^ association list
+          -> c e              -- ^ result
+
 --------------------------------------------------------------------------
 
 instance Container Vector Float where
@@ -167,6 +175,7 @@ instance Container Vector Float where
     step = stepF
     find = findV
     assoc = assocV
+    accum = accumV
     cond = condV condF
 
 instance Container Vector Double where
@@ -194,6 +203,7 @@ instance Container Vector Double where
     step = stepD
     find = findV
     assoc = assocV
+    accum = accumV
     cond = condV condD
 
 instance Container Vector (Complex Double) where
@@ -221,6 +231,7 @@ instance Container Vector (Complex Double) where
     step = undefined -- cannot match
     find = findV
     assoc = assocV
+    accum = accumV
     cond = undefined -- cannot match
 
 instance Container Vector (Complex Float) where
@@ -248,6 +259,7 @@ instance Container Vector (Complex Float) where
     step = undefined -- cannot match
     find = findV
     assoc = assocV
+    accum = accumV
     cond = undefined -- cannot match
 
 ---------------------------------------------------------------
@@ -281,6 +293,7 @@ instance (Container Vector a) => Container Matrix a where
     step = liftMatrix step
     find = findM
     assoc = assocM
+    accum = accumM
     cond = condM
 
 ----------------------------------------------------
@@ -637,6 +650,16 @@ assocM (r,c) z xs = ST.runSTMatrix $ do
         mapM_ (\((i,j),x) -> ST.writeMatrix m i j x) xs
         return m
 
+accumV v0 f xs = ST.runSTVector $ do
+        v <- ST.thawVector v0
+        mapM_ (\(k,x) -> ST.modifyVector v k (f x)) xs
+        return v
+
+accumM m0 f xs = ST.runSTMatrix $ do
+        m <- ST.thawMatrix m0
+        mapM_ (\((i,j),x) -> ST.modifyMatrix m i j (f x)) xs
+        return m
+
 ----------------------------------------------------------------------
 
 condM a b l e t = reshape (cols a'') $ cond a' b' l' e' t'
diff --git a/lib/Numeric/LinearAlgebra/Tests.hs b/lib/Numeric/LinearAlgebra/Tests.hs
index 3bcfec5..32cd39d 100644
--- a/lib/Numeric/LinearAlgebra/Tests.hs
+++ b/lib/Numeric/LinearAlgebra/Tests.hs
@@ -392,6 +392,18 @@ conformTest = utest "conform" ok
 
 ---------------------------------------------------------------------
 
+accumTest = utest "accum" ok
+  where
+    x = ident 3 :: Matrix Double
+    ok = accum x (+) [((1,2),7), ((2,2),3)]
+         == (3><3) [1,0,0
+                   ,0,1,7
+                   ,0,0,4]
+         &&
+         toList (flatten x) == [1,0,0,0,1,0,0,0,1] 
+
+---------------------------------------------------------------------
+
 -- | All tests must pass with a maximum dimension of about 20
 --  (some tests may fail with bigger sizes due to precision loss).
 runTests :: Int  -- ^ maximum dimension
@@ -562,6 +574,7 @@ runTests n = do
         , findAssocTest
         , condTest
         , conformTest
+        , accumTest
         ]
     return ()