# [pgrouting-users] algo which allow negative cost

Stephen Woodbridge woodbri at swoodbridge.com
Mon Jul 8 09:25:04 PDT 2013

```Why not just add 1.0 to all you edge costs so you minimum edge cost is 0
for fruits and 1+ for all other edges?

I assume that a -1 cost just means that the edge is desirable to capture
but is your goal is to collect some number of POI in an area, than it
might be better to get the location of all the POI and the cost to get
from each POI to each of the other POI then you can build a distance
matrix to compute TSP solution which is the minimum cost to hit every POI.

It is not clear to be what you want to achieve here. We do not have
algorithms targeted at game theory or solving game like problems. So you
have to re-map the problem into point to point shortest distance and
multiple point order optimization problems.

-Steve

On 7/8/2013 12:19 PM, Yaron Lev wrote:
> Hi,
>
> i am wondering if there is any algo within pgrouting 2, which will allow
> edges to have negative costs (without negative circles)?
>
> i was not able to find such, and in this event, is there some clever
> way, to achieve a similar effect?
>
> in specific, i am trying to solve a pac-man like problem.
>
> trying to find best route, given graph, where on some edges there are
> "fruits" to collect, collecting fruits will have a positive effect.
>
> your goal to collect as many fruits as possible, fruit can have a -1
> cost for example while each edge has it length as a positive cost.
>
> the outcome should be a route, where at any distance(this is flexible,
> as long as it achieve a similar goal) from route, the outcome route will
> have the best score out of all other routes.
>
> i tried using shortest path algo, with out negative costs, but i am
> unable to come up with a solution which will indeed provide such or
> similar solution. (in specfic un able to come up with costs, which will
> indeed "force" the route to collect those "fruits")
>
> i will appreciate any insight or direction for solving this problem.
>
>
> * the fruits are actually poi, such as bus stations, museums etc.
> * if negative edge costs are allowed, the problem is solved.
>