covd.md
In ricci: Ricci Calculus

covd input validation works

Code
  covd(arr %_% .(i, j), .(k), g = g_eucl_cart(2))
Condition
  Error in `covd()`:
  ! Incorrect tensor dimension.
  x Indices i and j need to match the dimensions of the metric tensor.
  i Dimension of metric tensor: 2
  i Dimension of i and j: 3 and 3
    Do you need to use the argument `act_on`?

Code
  covd(arr %_% .(i, j), .(k), g = g_eucl_cart(2), act_on = .(l))
Condition
  Error in `covd()`:
  ! Argument `act_on` contains invalid index.
  x Index `l` not present in <Labeled Array> [3x3] .(-i, -j).
  i Make sure you only select indices that match the tensor indices.