Assume graph as:

Whent the demand of A,B,C = 0. The input slot ratio of D (input slot A-D, B-D, C-D) should be able to calculate and not throw a "SystemStackError: stack level too deep".
Suggestions for solving this:
- Take 1 /
amount of nodes (in the example 3) as the default input share
- Set the first nodes input slot to 1, all the others to zero
Related issue: quintel/etlocal#73