Thanks Anna and Doug,
I did not expect it to work (thought it would be useful if it did). Rather I
was surprised by the fact that r.walk DID run and that it gave very odd results.
Adding to the docs is a good idea. Even better would also to have a friction
map with a negative value (min<0)
I think r.walk was not written for negative friction and while I imagine
some small (in absolute sense) negative values may work, your negative
values are pretty extreme, meaning the resulting travel time through a cell
would be negative. That can cause all kinds of issues in the algorithm. So
I
