2 files changed, 28 insertions, 0 deletions

diff --git a/lib/Data/Packed/Internal/Matrix.hs b/lib/Data/Packed/Internal/Matrix.hs
index 86c5915..1c58f6e 100644
--- a/lib/Data/Packed/Internal/Matrix.hs
+++ b/lib/Data/Packed/Internal/Matrix.hs
@@ -385,3 +385,30 @@ fromFile filename (r,c) = do
     --free charname  -- TO DO: free the auxiliary CString
     return res
 foreign import ccall "auxi.h matrix_fscanf" c_gslReadMatrix:: Ptr CChar -> TM
+
+----------------------------------------------------------------------------
+
+{- | creates a new matrix with the given position updated with a modification function
+
+@> updateMatrix (0,2) (const 57) (ident 3 :: Matrix Double)
+(3><3)
+ [ 1.0, 0.0, 57.0
+ , 0.0, 1.0,  0.0
+ , 0.0, 0.0,  1.0 ]@
+
+-}
+updateMatrix :: Storable t
+             => (Int,Int) -- ^ position (row,column)
+             -> (t -> t)  -- ^ modification function
+             -> Matrix t  -- ^ source matrix
+             -> Matrix t  -- ^ result
+
+updateMatrix (i,j) f (m@MC {rows = r, cols = c, cdat = v})
+    | i<0 || i>=r || j<0 || j>=c = error $ "updateMatrix out of range(size="++show (r,c)++", pos="++show (i,j)++")"
+    | otherwise                  = let pos = i*c+j
+                                    in m { cdat = updateVector pos f v }
+
+updateMatrix (i,j) f (m@MF {rows = r, cols = c, fdat = v})
+    | i<0 || i>=r || j<0 || j>=c = error $ "updateMatrix out of range(size="++show (r,c)++", pos="++show (i,j)++")"
+    | otherwise                  = let pos = j*r+i
+                                    in m { fdat = updateVector pos f v }
diff --git a/lib/Data/Packed/Matrix.hs b/lib/Data/Packed/Matrix.hs
index 62d28b1..b2e58b5 100644
--- a/lib/Data/Packed/Matrix.hs
+++ b/lib/Data/Packed/Matrix.hs
@@ -28,6 +28,7 @@ module Data.Packed.Matrix (
     subMatrix, takeRows, dropRows, takeColumns, dropColumns,
     extractRows,
     ident, diag, diagRect, takeDiag,
+    updateMatrix,
     liftMatrix, liftMatrix2,
     format, readMatrix, fromFile, fromArray2D
 ) where