precompute partial distance matrices

[benj919]

Currently the distance matrices can only be left out or computed fully during the input creation.

We may want to offer calculating partial/full distance matrices from existing inputs.

[ohagen]

@benj919 is this still so?

[benj919]

yes, this is currently a proposal only

[ohagen]

I think this goes with #36 .. it's what I was thinking at the time. I have a code for this