Stephan Dempe - Academia.edu (original) (raw)
Papers by Stephan Dempe
International Journal of Operational Research/Nepal
Contraflow evacuation planning strategy is very effective and widely accepted approach for the op... more Contraflow evacuation planning strategy is very effective and widely accepted approach for the optimal use of available road network in evacuation management that increases the outward road capacities from the disastrous areas with lane (arc) reversals towards the safer places. It is highly applicable for shifting maximum number of evacuees from the disastrous areas to the safer places as quickly and efficiently as possible. We introduce the partial contraflow approach by reversing only necessary arc capacities to solve the earliest arrival contraflow problem with constant transit times and present efficient algorithms. We solve the earliest arrival partial contraflow problem in two terminal general network in pseudo-polynomial time complexity. On two terminal series parallel network, we solve the problem in strongly polynomial time complexity. Moreover, we present a fully polynomial approximation algorithm that solves the earliest arrival partial contraflow problem on two terminal ...
Lineare Optimierung, 2010
Springer Optimization and Its Applications, 2010
The Nepali Mathematical Sciences Report, 2021
Contraflow is one of the best and widely accepted techniques in evacuation planning problems, whe... more Contraflow is one of the best and widely accepted techniques in evacuation planning problems, where the reversal of arcs is made to increase the amount and decrease the time of ow transmission. At the time of evacuation, if the flow value leaving the source node exceeds the bottleneck capacity of the network, then the storage of excess flow at comparatively safer intermediate nodes can be a milestone to save the life of evacuees. In this paper, we introduce the maximum dynamic contraflow problem in a general network and earliest arrival contraflow problem in two-terminal series-parallel network with asymmetric transit times on anti-parallel arcs. We present polynomial time solution strategies with orientation dependent transit times by allowing the storage of flow at intermediate nodes.
Multi-commodity flow problems concern with the transshipment of more than one com13 modities from... more Multi-commodity flow problems concern with the transshipment of more than one com13 modities from respective sources to the corresponding sinks without violating the capacity con14 straints on the arcs. If the objective of the problem is to send the maximum amount of flow within 15 given time horizon, then it becomes the maximum flow problem. In multi-commodity flow prob16 lem, flow of different commodities departing from their sources arrive at the common intermediate 17 node and have to share the capacity through the arc. The sharing of the capacity in the common arc 18 (bundle arc) is one of the major issues in the multi-commodity flow problems. In this paper, we 19 introduce the maximum static and maximum dynamic multi-commodity flow problems with pro20 portional capacity sharing and present polynomial time algorithms to solve the problems. Similarly, 21 we investigate the maximum dynamic multi-commodity flow problem with flow-dependent capac22 ity sharing and present a pseudo-p...
IOCA 2021, 2021
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Computer Sciences & Mathematics Forum, 2021
Multi-commodity flow problems concerned with the transshipment of more than one commodity from re... more Multi-commodity flow problems concerned with the transshipment of more than one commodity from respective sources to the corresponding sinks without violating the capacity constraints on the arcs. If the objective of the problem is to send the maximum amount of flow within a given time horizon, then it becomes the maximum flow problem. In multi-commodity flow problems, the flow of different commodities departing from their sources arriving at the common intermediate node have to share the capacity through the arc. The sharing of the capacity in the common arc (bundle arc) is one of the major issues in the multi-commodity flow problems. In this paper, we introduce the maximum static and maximum dynamic multi-commodity flow problems with proportional capacity sharing and present polynomial time algorithms to solve the problems. Similarly, we investigate the maximum dynamic multi-commodity flow problems with flow-dependent capacity sharing and present a pseudo-polynomial time solution ...
SN Operations Research Forum, 2020
Various network flow models have been extensively investigated during more than a half century. I... more Various network flow models have been extensively investigated during more than a half century. In most cases, flow maximization, time minimization, cost minimization or a combination of them are considered subject to the flow conservation constraints, i.e., inflow should be equal to outflow on each node except the sources and sinks. In this paper, we investigate the network flow models with intermediate storage, i.e., the inflow may be greater than the outflow on intermediate nodes. We suggest strongly polynomial time algorithms in both static and dynamic maximum flow problems on two terminal general networks. We also study the earliest arrival property of the maximum dynamic flow on two terminal series-parallel networks and solve the earliest arrival flow problem in polynomial time complexity. Moreover, we investigate the dynamic contraflow model and present polynomial time algorithms to solve the maximum dynamic contraflow and the earliest arrival contraflow problems on general two terminal and series-parallel networks.
The contraflow techniques have widely been effective in evacuation planning research. We present ... more The contraflow techniques have widely been effective in evacuation planning research. We present efficient algorithms to solve the evacuation network flow problems, namely, the maximum, earliest arrival, quickest and lex-maximum dynamic contraflow problems having constant attributes and their generalizations with partial contraflow reconfiguration. Moreover, the contraflow models with inflow dependent and load dependent transit times are introduced and presented strongly polynomial time algorithms to compute approximation solutions of the corresponding quickest contraflow problems on two terminal networks with partial reversals of arc capacities. Our results on partial lane reversals should be quite relevant for reducing evacuation time and supporting logistics in emergencies.
We consider an optimistic semivectorial bilevel programming problem in Banach spaces. The associa... more We consider an optimistic semivectorial bilevel programming problem in Banach spaces. The associated lower level multicriterial optimization problem is assumed to be convex w.r.t. its decision variable. This property implies that all its weakly ecient points can be computed applying the weighted-sumscalarization technique. Consequently, it is possible to replace the overall semivectorial bilevel programming problem by means of a standard bilevel programming problem whose upper level variables comprise the set of suitable scalarization parameters for the lower level problem. In this note, we consider the relationship between this surrogate bilevel programming problem and the original semivectorial bilevel programming problem. As it will be shown, this is a delicate issue as long as locally optimal solutions are investigated. The obtained theory is applied in order to derive existence results for semivectorial bilevel programming problems with not necessarily nite-dimensional lower level decision variables. Some regarding examples from bilevel optimal control are presented.
Journal of Industrial & Management Optimization, 2017
Dynamic network flow problems have wide applications in evacuation planning. From a given subset ... more Dynamic network flow problems have wide applications in evacuation planning. From a given subset of arcs in a directed network, choosing the suitable arcs for facility location is very important in the optimization of flows in emergency cases. Because of the decrease in the capacity of an arc by placing a facility in it, there may be a reduction in the maximum flow or increase in the quickest time. In this work, we consider a problem of identifying the optimal facility locations so that the increase in the quickest time is minimum. Introducing the quickest FlowLoc problem, we give strongly polynomial time algorithms to solve the single facility case. Realizing NP-hardness of the multi-facility case, we develop a mixed integer programming formulation of it and give a polynomial time heuristic for its solution. Because of the growing concerns of arc reversals in evacuation planning, we introduce quickest Con-traFlowLoc problem and present exact algorithms to solve single-facility case and a heuristic to solve the multi-facility case, both of which have polynomial time complexity. The solutions thus obtained here are practically important, particularly in evacuation planning, to systematize traffic flow with facility allocation minimizing evacuation time.
Positivity, 2019
In this paper, we have pointed out that the proof of Theorem 11 in the recent paper (Lafhim in Po... more In this paper, we have pointed out that the proof of Theorem 11 in the recent paper (Lafhim in Positivity, 2019.
SIAM Journal on Optimization, 2018
In this paper, we consider optimistic bilevel programming problems whose lower level is a semidef... more In this paper, we consider optimistic bilevel programming problems whose lower level is a semidefinite programming problem. Three main approaches namely, the optimal value reformulation, the Karush-Kuhn-Tucker one single level reformulation, and the replacement of the lower level by a generalized equation are considered in order to transform the original problem into a single level programming problem. Afterwards, the relationship between the original problem and its substitute is studied in each case and some necessary optimality conditions are derived as well. Later on, we obtain some optimality conditions without any hypothesis on convexity by using the optimal value reformulation.
SIAM Journal on Optimization, 2016
This paper focuses on the development of optimality conditions for a bilevel optimal control prob... more This paper focuses on the development of optimality conditions for a bilevel optimal control problem with pure state constrains in the upper level and a finite-dimensional parametric optimization problem in the lower level. After transforming the problem into an equivalent single-level problem we concentrate on the derivation of a necessary optimality condition of Pontryagin-type. We point out some major difficulties arising from the bilevel structure of the original problem and its pure state constraints in the upper level leading to a degenerated maximum principle in the absence of constraint qualifications. Hence, we use a partial penalization approach and a well-known regularity condition for optimal control problems with pure state constraints to ensure the non-degeneracy of the derived maximum principle. Finally, we illustrate the applicability of the derived theory by means of a small example.
Computational Optimization and Applications, 2015
An algorithm is presented for solving bilevel optimization problems with fully convex lower level... more An algorithm is presented for solving bilevel optimization problems with fully convex lower level problems. Convergence to a local optimal solution is shown under certain weak assumptions. This algorithm uses the optimal value transformation of the problem. Transformation of the bilevel optimization problem using the Fritz-John necessary optimality conditions applied to the lower level problem is shown to exhibit almost the same difficulties for solving the problem as the use of the Karush-Kuhn-Tucker conditions.
Nonconvex Optimization and Its Applications, 1998
... of Theorem 2.3 that the directional derivative of x (.) is a PC1 function of the direction wh... more ... of Theorem 2.3 that the directional derivative of x (.) is a PC1 function of the direction where the ... has a unique local optimal solution x/(y) with y= y+ tr which is also feasible for the ... One such method, which has successfully be applied is the bundle-trust region algorithm [17, 18, 27 ...
Operations Research ’92, 1993
Consider a situation where two decision makers try to realize best decisions with respect to thei... more Consider a situation where two decision makers try to realize best decisions with respect to their own objective functions thereby acting in an hierarchical manner. Assume that the first decision maker’s (the leader’s) choice y influences the second one’s (the follower’s) objective function as well as his set of admissible decisions.
Lineare Optimierung, 2010
ABSTRACT Lineare Optimierungsaufgaben treten auf natüurliche Weise in vielen Anwendungen auf, wie... more ABSTRACT Lineare Optimierungsaufgaben treten auf natüurliche Weise in vielen Anwendungen auf, wie zunäachst an einer klassischen Situation demonstriert wird.
International Journal of Operational Research/Nepal
Contraflow evacuation planning strategy is very effective and widely accepted approach for the op... more Contraflow evacuation planning strategy is very effective and widely accepted approach for the optimal use of available road network in evacuation management that increases the outward road capacities from the disastrous areas with lane (arc) reversals towards the safer places. It is highly applicable for shifting maximum number of evacuees from the disastrous areas to the safer places as quickly and efficiently as possible. We introduce the partial contraflow approach by reversing only necessary arc capacities to solve the earliest arrival contraflow problem with constant transit times and present efficient algorithms. We solve the earliest arrival partial contraflow problem in two terminal general network in pseudo-polynomial time complexity. On two terminal series parallel network, we solve the problem in strongly polynomial time complexity. Moreover, we present a fully polynomial approximation algorithm that solves the earliest arrival partial contraflow problem on two terminal ...
Lineare Optimierung, 2010
Springer Optimization and Its Applications, 2010
The Nepali Mathematical Sciences Report, 2021
Contraflow is one of the best and widely accepted techniques in evacuation planning problems, whe... more Contraflow is one of the best and widely accepted techniques in evacuation planning problems, where the reversal of arcs is made to increase the amount and decrease the time of ow transmission. At the time of evacuation, if the flow value leaving the source node exceeds the bottleneck capacity of the network, then the storage of excess flow at comparatively safer intermediate nodes can be a milestone to save the life of evacuees. In this paper, we introduce the maximum dynamic contraflow problem in a general network and earliest arrival contraflow problem in two-terminal series-parallel network with asymmetric transit times on anti-parallel arcs. We present polynomial time solution strategies with orientation dependent transit times by allowing the storage of flow at intermediate nodes.
Multi-commodity flow problems concern with the transshipment of more than one com13 modities from... more Multi-commodity flow problems concern with the transshipment of more than one com13 modities from respective sources to the corresponding sinks without violating the capacity con14 straints on the arcs. If the objective of the problem is to send the maximum amount of flow within 15 given time horizon, then it becomes the maximum flow problem. In multi-commodity flow prob16 lem, flow of different commodities departing from their sources arrive at the common intermediate 17 node and have to share the capacity through the arc. The sharing of the capacity in the common arc 18 (bundle arc) is one of the major issues in the multi-commodity flow problems. In this paper, we 19 introduce the maximum static and maximum dynamic multi-commodity flow problems with pro20 portional capacity sharing and present polynomial time algorithms to solve the problems. Similarly, 21 we investigate the maximum dynamic multi-commodity flow problem with flow-dependent capac22 ity sharing and present a pseudo-p...
IOCA 2021, 2021
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Computer Sciences & Mathematics Forum, 2021
Multi-commodity flow problems concerned with the transshipment of more than one commodity from re... more Multi-commodity flow problems concerned with the transshipment of more than one commodity from respective sources to the corresponding sinks without violating the capacity constraints on the arcs. If the objective of the problem is to send the maximum amount of flow within a given time horizon, then it becomes the maximum flow problem. In multi-commodity flow problems, the flow of different commodities departing from their sources arriving at the common intermediate node have to share the capacity through the arc. The sharing of the capacity in the common arc (bundle arc) is one of the major issues in the multi-commodity flow problems. In this paper, we introduce the maximum static and maximum dynamic multi-commodity flow problems with proportional capacity sharing and present polynomial time algorithms to solve the problems. Similarly, we investigate the maximum dynamic multi-commodity flow problems with flow-dependent capacity sharing and present a pseudo-polynomial time solution ...
SN Operations Research Forum, 2020
Various network flow models have been extensively investigated during more than a half century. I... more Various network flow models have been extensively investigated during more than a half century. In most cases, flow maximization, time minimization, cost minimization or a combination of them are considered subject to the flow conservation constraints, i.e., inflow should be equal to outflow on each node except the sources and sinks. In this paper, we investigate the network flow models with intermediate storage, i.e., the inflow may be greater than the outflow on intermediate nodes. We suggest strongly polynomial time algorithms in both static and dynamic maximum flow problems on two terminal general networks. We also study the earliest arrival property of the maximum dynamic flow on two terminal series-parallel networks and solve the earliest arrival flow problem in polynomial time complexity. Moreover, we investigate the dynamic contraflow model and present polynomial time algorithms to solve the maximum dynamic contraflow and the earliest arrival contraflow problems on general two terminal and series-parallel networks.
The contraflow techniques have widely been effective in evacuation planning research. We present ... more The contraflow techniques have widely been effective in evacuation planning research. We present efficient algorithms to solve the evacuation network flow problems, namely, the maximum, earliest arrival, quickest and lex-maximum dynamic contraflow problems having constant attributes and their generalizations with partial contraflow reconfiguration. Moreover, the contraflow models with inflow dependent and load dependent transit times are introduced and presented strongly polynomial time algorithms to compute approximation solutions of the corresponding quickest contraflow problems on two terminal networks with partial reversals of arc capacities. Our results on partial lane reversals should be quite relevant for reducing evacuation time and supporting logistics in emergencies.
We consider an optimistic semivectorial bilevel programming problem in Banach spaces. The associa... more We consider an optimistic semivectorial bilevel programming problem in Banach spaces. The associated lower level multicriterial optimization problem is assumed to be convex w.r.t. its decision variable. This property implies that all its weakly ecient points can be computed applying the weighted-sumscalarization technique. Consequently, it is possible to replace the overall semivectorial bilevel programming problem by means of a standard bilevel programming problem whose upper level variables comprise the set of suitable scalarization parameters for the lower level problem. In this note, we consider the relationship between this surrogate bilevel programming problem and the original semivectorial bilevel programming problem. As it will be shown, this is a delicate issue as long as locally optimal solutions are investigated. The obtained theory is applied in order to derive existence results for semivectorial bilevel programming problems with not necessarily nite-dimensional lower level decision variables. Some regarding examples from bilevel optimal control are presented.
Journal of Industrial & Management Optimization, 2017
Dynamic network flow problems have wide applications in evacuation planning. From a given subset ... more Dynamic network flow problems have wide applications in evacuation planning. From a given subset of arcs in a directed network, choosing the suitable arcs for facility location is very important in the optimization of flows in emergency cases. Because of the decrease in the capacity of an arc by placing a facility in it, there may be a reduction in the maximum flow or increase in the quickest time. In this work, we consider a problem of identifying the optimal facility locations so that the increase in the quickest time is minimum. Introducing the quickest FlowLoc problem, we give strongly polynomial time algorithms to solve the single facility case. Realizing NP-hardness of the multi-facility case, we develop a mixed integer programming formulation of it and give a polynomial time heuristic for its solution. Because of the growing concerns of arc reversals in evacuation planning, we introduce quickest Con-traFlowLoc problem and present exact algorithms to solve single-facility case and a heuristic to solve the multi-facility case, both of which have polynomial time complexity. The solutions thus obtained here are practically important, particularly in evacuation planning, to systematize traffic flow with facility allocation minimizing evacuation time.
Positivity, 2019
In this paper, we have pointed out that the proof of Theorem 11 in the recent paper (Lafhim in Po... more In this paper, we have pointed out that the proof of Theorem 11 in the recent paper (Lafhim in Positivity, 2019.
SIAM Journal on Optimization, 2018
In this paper, we consider optimistic bilevel programming problems whose lower level is a semidef... more In this paper, we consider optimistic bilevel programming problems whose lower level is a semidefinite programming problem. Three main approaches namely, the optimal value reformulation, the Karush-Kuhn-Tucker one single level reformulation, and the replacement of the lower level by a generalized equation are considered in order to transform the original problem into a single level programming problem. Afterwards, the relationship between the original problem and its substitute is studied in each case and some necessary optimality conditions are derived as well. Later on, we obtain some optimality conditions without any hypothesis on convexity by using the optimal value reformulation.
SIAM Journal on Optimization, 2016
This paper focuses on the development of optimality conditions for a bilevel optimal control prob... more This paper focuses on the development of optimality conditions for a bilevel optimal control problem with pure state constrains in the upper level and a finite-dimensional parametric optimization problem in the lower level. After transforming the problem into an equivalent single-level problem we concentrate on the derivation of a necessary optimality condition of Pontryagin-type. We point out some major difficulties arising from the bilevel structure of the original problem and its pure state constraints in the upper level leading to a degenerated maximum principle in the absence of constraint qualifications. Hence, we use a partial penalization approach and a well-known regularity condition for optimal control problems with pure state constraints to ensure the non-degeneracy of the derived maximum principle. Finally, we illustrate the applicability of the derived theory by means of a small example.
Computational Optimization and Applications, 2015
An algorithm is presented for solving bilevel optimization problems with fully convex lower level... more An algorithm is presented for solving bilevel optimization problems with fully convex lower level problems. Convergence to a local optimal solution is shown under certain weak assumptions. This algorithm uses the optimal value transformation of the problem. Transformation of the bilevel optimization problem using the Fritz-John necessary optimality conditions applied to the lower level problem is shown to exhibit almost the same difficulties for solving the problem as the use of the Karush-Kuhn-Tucker conditions.
Nonconvex Optimization and Its Applications, 1998
... of Theorem 2.3 that the directional derivative of x (.) is a PC1 function of the direction wh... more ... of Theorem 2.3 that the directional derivative of x (.) is a PC1 function of the direction where the ... has a unique local optimal solution x/(y) with y= y+ tr which is also feasible for the ... One such method, which has successfully be applied is the bundle-trust region algorithm [17, 18, 27 ...
Operations Research ’92, 1993
Consider a situation where two decision makers try to realize best decisions with respect to thei... more Consider a situation where two decision makers try to realize best decisions with respect to their own objective functions thereby acting in an hierarchical manner. Assume that the first decision maker’s (the leader’s) choice y influences the second one’s (the follower’s) objective function as well as his set of admissible decisions.
Lineare Optimierung, 2010
ABSTRACT Lineare Optimierungsaufgaben treten auf natüurliche Weise in vielen Anwendungen auf, wie... more ABSTRACT Lineare Optimierungsaufgaben treten auf natüurliche Weise in vielen Anwendungen auf, wie zunäachst an einer klassischen Situation demonstriert wird.