added mapCols, mapRows, sumColsBy and sumRowsBy to Matrix F# module (for symmetry with sumBy from the List, Array and Seq modules)

src/FSharp/Matrix.fs

@@ -126,6 +126,14 @@ module Matrix =
                 C.[i,j] <- f i j (C.Item(i,j))
         C
     
+    /// Map every matrix column into an element in a sequence using the given position dependent function.
+    let inline mapCols (f: int -> Vector<float> -> 'a) (A: #Matrix<float>) =
+        A.ColumnEnumerator() |> Seq.map (fun (j, row) -> f j row)
+
+    /// Map every matrix row into an element in a sequence using the given position dependent function.
+    let inline mapRows (f: int -> Vector<float> -> 'a) (A: #Matrix<float>) =
+        A.RowEnumerator() |> Seq.map (fun (i, row) -> f i row)
+
     /// In-place assignment.
     let inline inplaceAssign (f: int -> int -> float) (A: #Matrix<float>) =
         for i=0 to A.RowCount-1 do
@@ -151,7 +159,15 @@ module Matrix =
             for j=0 to A.ColumnCount-1 do
                 f <- f + A.Item(i,j)
         f
+
+    /// Returns the sum of the results generated by applying the function to each column of the matrix.
+    let inline sumColsBy (f: int -> Vector<float> -> float) (A: #Matrix<float>) =
+        mapCols f A |> Seq.fold (+) 0.0
     
+    /// Returns the sum of the results generated by applying the function to each row of the matrix.
+    let inline sumRowsBy (f: int -> Vector<float> -> float) (A: #Matrix<float>) =
+        mapRows f A |> Seq.fold (+) 0.0
+
     /// Iterates over all elements of a matrix.
     let inline iter (f: float -> unit) (A: #Matrix<float>) =
         for i=0 to A.RowCount-1 do