FSharp: support new F#3.1 slicing getters on matrices (setters prepared as well)

src/FSharp/LinearAlgebra.fs

@@ -85,3 +85,31 @@ module FSharpExtensions =
       let cfinish = defaultArg cfinish (x.ColumnCount - 1)
       let rfinish = defaultArg rfinish (x.RowCount - 1)
       x.SetSubMatrix(rstart, rfinish - rstart + 1, cstart, cfinish - cstart + 1, values)
+
+    /// Gets a row subvector using a specified row index and column range.
+    /// This method can be used via the x.[r, c1 .. c2] syntax (F#3.1)
+    member x.GetSlice(r, cstart, cfinish) =
+      let cstart = defaultArg cstart 0
+      let cfinish = defaultArg cfinish (x.ColumnCount - 1)
+      x.Row(r, cstart, cfinish - cstart + 1)
+
+    /// Gets a column subvector using a specified row index and column range.
+    /// This method can be used via the x.[r, c1 .. c2] syntax (F#3.1)
+    member x.GetSlice(rstart, rfinish, c) =
+      let rstart = defaultArg rstart 0
+      let rfinish = defaultArg rfinish (x.RowCount - 1)
+      x.Column(c, rstart, rfinish - rstart + 1)
+
+//    /// Sets a row subvector using a specified row index and column range.
+//    /// This method can be used via the x.[r, c1 .. c2] <- v syntax (F#3.1)
+//    member x.GetSlice(r, cstart, cfinish, values) =
+//      let cstart = defaultArg cstart 0
+//      let cfinish = defaultArg cfinish (x.ColumnCount - 1)
+//      x.SetRow(r, cstart, cfinish - cstart + 1, values)
+//
+//    /// Sets a column subvector using a specified row index and column range.
+//    /// This method can be used via the x.[r, c1 .. c2] <- v syntax (F#3.1)
+//    member x.GetSlice(rstart, rfinish, c, values) =
+//      let rstart = defaultArg rstart 0
+//      let rfinish = defaultArg rfinish (x.RowCount - 1)
+//      x.SetColumn(c, rstart, rfinish - rstart + 1, values)