Using an Array in a While Loop

[JakeWitten]

Is my understanding correct that the F force calculated for each pair, e.g. i=0, j=1 is net, i.e. no need to calculate also for i=1, j=0?

Yes, its net.
It didn't occur to me that the nested loop would cycle through the full range of j for every i value, so that's not the problem...
I still don't know what the issue is then. It kind of looks like the force from the sun isn't being accounted for, but I don't see why it wouldn't be.