id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	revision
663	Getting the node potentials in min cost flow	matheusota	Alpar Juttner	"Hi,

I'm interested in getting the dual solution of a min-cost s-t flow problem. I executed the Network Simplex algorithm using


{{{
NS::ProblemType status = ns.run()
}}}


and afterwards I set the node potentials with


{{{
ns.potentialMap(dualNodeValues)
}}}


However, when I compute the objective function of the dual (by setting the dual of each edge to be the maximum between 0 and the negative of the reduced cost), it does not match the objective function of the primal (the value of the min-cost flow). I'm suspecting that, because the problem was solved in a single iteration (after finding a max-flow), the duals are not correctly set.

I say that because, in my understanding, the duals should be the value of the shortest paths starting at t in the residual graph. So I computed these by hand and it does not match the values I obtain from lemon. Is there a way that I can update the dual values (without me having to manually create the residual graph and running a shortest path algorithm)?

Thanks!
Matheus"	defect	closed	major	LEMON 1.4 release	core	hg main	invalid