rename compute_one to compute_up

I'm pulling apart #549 to a few PRs.  This one renames `compute_one` to `compute_up` to match against `compute_down` which was added a while ago.

Note that this work was done a while ago, so in merging I may have overwritten a thing or two.  This deserves some attention.  
maybe

```python
scope=None
```
in the signature then

```python
if scope is None:
    scope = {}
```