arXiv subjects

Qian-Ping Gu

Publications and source records attributed to Qian-Ping Gu.

7 recordsLinked to original sources

arXiv2025

Exact Set Packing in Multimodal Transportation with Ridesharing System for First/Last Mile

We propose a centralized transportation system that integrates public transit with ridesharing to provide multimodal transportation. At each time interval, the system receives a set of personal drivers, designated drivers, and public transit riders. It then assigns all riders to drivers, ensuring that pick-ups and drop-offs occur at designated transit stations. This effectively replaces first-mile/last-mile (FM/LM) segments with a ridesharing alternative, reducing overall commuting time. We study two optimization problems: (1) minimizing the total travel distances of drivers and (2) minimizing the number of designated drivers required to serve all riders. We show the optimization problems are NP-hard and give hypergraph-based integer linear programming exact algorithm and approximation algorithms. To enhance computational efficiency, we introduce a clustering heuristic that utilizes both spatial and temporal aspects of the input data to accelerate rider-to-driver assignments. Finally, we conduct an extensive computational study using real-world datasets and surveys from Chicago to evaluate our model and algorithms at a city-wide scale.

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arXiv2023

Algorithms for the Ridesharing with Profit Constraint Problem

Mobility-on-demand (MoD) ridesharing is a promising way to improve the occupancy rate of personal vehicles and reduce traffic congestion and emissions. Maximizing the number of passengers served and maximizing a profit target are major optimization goals in MoD ridesharing. We study the ridesharing with profit constraint problem (labeled as RPC) which considers both optimization goals altogether: maximize the total number of passengers subject to an overall drivers' profit target. We give a mathematical formulation for the RPC problem. We present a polynomial-time exact algorithm framework (including two practical implementations of the algorithm) and a (1/2)-approximation algorithm for the case that each vehicle serves at most one passenger. We propose a (2/3*lambda)-approximation algorithm for the case that each vehicle serves at most lambda >= 2 passengers. Our algorithms revolve around the idea of maximum cardinality matching in bipartite graphs and hypergraphs (set packing) with general edge weight. Based on a real-world ridesharing dataset in Chicago City and price schemes of Uber, we conduct an extensive empirical study on our model and algorithms. Experimental results show that practical price schemes can be incorporated into our model, our exact algorithms are efficient, and our approximation algorithms achieve about 90% of optimal solutions, in the number of passengers served.

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arXiv2023

Algorithms and Computational Study on a Transportation System Integrating Public Transit and Ridesharing of Personal Vehicles

The potential of integrating public transit with ridesharing includes shorter travel time for commuters and higher occupancy rate of personal vehicles and public transit ridership. In this paper, we describe a centralized transit system that integrates public transit and ridesharing to reduce travel time for commuters. In the system, a set of ridesharing providers (drivers) and a set of public transit riders are received. The optimization goal of the system is to assign riders to drivers by arranging public transit and ridesharing combined routes subject to shorter commuting time for as many riders as possible. We give an exact algorithm, which is an ILP formulation based on a hypergraph representation of the problem. By using the ILP and the hypergraph, we give approximation algorithms based on LP-rounding and hypergraph matching/weighted set packing, respectively. As a case study, we conduct an extensive computational study based on real-world public transit dataset and ridesharing dataset in Chicago city. To evaluate the effectiveness of the transit system and our algorithms, we generate data instances from the datasets. The experimental results show that more than 60% of riders are assigned to drivers on average, riders' commuting time is reduced by 23% and vehicle occupancy rate is improved to almost 3. Our proposed algorithms are efficient for practical scenarios.

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arXiv2021

Multimodal Transportation with Ridesharing of Personal Vehicles

Many public transportation systems are unable to keep up with growing passenger demand as the population grows in urban areas. The slow or lack of improvements for public transportation pushes people to use private transportation modes, such as carpooling and ridesharing. However, the occupancy rate of personal vehicles has been dropping in many cities. In this paper, we describe a centralized transit system that integrates public transit and ridesharing, which matches drivers and transit riders such that the riders would result in shorter travel time using both transit and ridesharing. The optimization goal of the system is to assign as many riders to drivers as possible for ridesharing. We give an exact approach and approximation algorithms to achieve the optimization goal. As a case study, we conduct an extensive computational study to show the effectiveness of the transit system for different approximation algorithms, based on the real-world traffic data in Chicago City; the data sets include both public transit and ridesharing trip information. The experiment results show that our system is able to assign more than 60% of riders to drivers, leading to a substantial increase in occupancy rate of personal vehicles and reducing riders' travel time.

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arXiv2021

Approximate Ridesharing of Personal Vehicles Problem

The ridesharing problem is that given a set of trips, each trip consists of an individual, a vehicle of the individual and some requirements, select a subset of trips and use the vehicles of selected trips to deliver all individuals to their destinations satisfying the requirements. Requirements of trips are specified by parameters including source, destination, vehicle capacity, preferred paths of a driver, detour distance and number of stops a driver is willing to make, and time constraints. We analyze the relations between the time complexity and parameters for two optimization problems: minimizing the number of selected vehicles and minimizing total travel distance of the vehicles. We consider the following conditions: (1) all trips have the same source or same destination, (2) no detour is allowed, (3) each participant has one preferred path, (4) no limit on the number of stops, and (5) all trips have the same departure and same arrival time. It is known that both minimization problems are NP-hard if one of Conditions (1), (2) and (3) is not satisfied. We prove that both problems are NP-hard and further show that it is NP-hard to approximate both problems within a constant factor if Conditions (4) or (5) is not satisfied. We give $\frac{K+2}{2}$-approximation algorithms for minimizing the number of selected vehicles when condition (4) is not satisfied, where $K$ is the largest capacity of all vehicles.

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arXiv2017

Constant Query Time $(1 + ε)$-Approximate Distance Oracle for Planar Graphs

We give a $(1+ε)$-approximate distance oracle with $O(1)$ query time for an undirected planar graph $G$ with $n$ vertices and non-negative edge lengths. For $ε>0$ and any two vertices $u$ and $v$ in $G$, our oracle gives a distance $\tilde{d}(u,v)$ with stretch $(1+ε)$ in $O(1)$ time. The oracle has size $O(n\log n ((\log n)/ε+f(ε)))$ and pre-processing time $O(n\log n((\log^3 n)/ε^2+f(ε)))$, where $f(ε)=2^{O(1/ε)}$. This is the first $(1+ε)$-approximate distance oracle with $O(1)$ query time independent of $ε$ and the size and pre-processing time nearly linear in $n$, and improves the query time $O(1/ε)$ of previous $(1+ε)$-approximate distance oracle with size nearly linear in $n$.

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arXiv2016

Near-Linear Time Constant-Factor Approximation Algorithm for Branch-Decomposition of Planar Graphs

We give an algorithm which for an input planar graph $G$ of $n$ vertices and integer $k$, in $\min\{O(n\log^3n),O(nk^2)\}$ time either constructs a branch-decomposition of $G$ with width at most $(2+δ)k$, $δ>0$ is a constant, or a $(k+1)\times \lceil{\frac{k+1}{2}\rceil}$ cylinder minor of $G$ implying $bw(G)>k$, $bw(G)$ is the branchwidth of $G$. This is the first $\tilde{O}(n)$ time constant-factor approximation for branchwidth/treewidth and largest grid/cylinder minors of planar graphs and improves the previous $\min\{O(n^{1+ε}),O(nk^2)\}$ ($ε>0$ is a constant) time constant-factor approximations. For a planar graph $G$ and $k=bw(G)$, a branch-decomposition of width at most $(2+δ)k$ and a $g\times \frac{g}{2}$ cylinder/grid minor with $g=\frac{k}β$, $β>2$ is constant, can be computed by our algorithm in $\min\{O(n\log^3n\log k),O(nk^2\log k)\}$ time.

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