The following generates a Vector of immutable Vectors:

```
var darr = Vector.tabulate(2, 3){ (a,b) => a*2+b }
darr: scala.collection.immutable.Vector[scala.collection.immutable.Vector[Int]] = Vector(Vector(0, 1, 2), Vector(2, 3, 4))

```

But what is needed for our use case is a Vector of *mutable* Vectors. How can that be done?