̽��ֱ�� of Cambridge - logistics

Improved approach to the ‘Travelling Salesperson Problem’ could improve logistics and transport sectors

sc604 — Tue, 26 Apr 2022 09:02:31 +0000

A notorious theoretical question that has puzzled researchers for 90 years, the Travelling Salesperson Problem also has real relevance to industry today. Essentially a question about how best to combine a set of tasks so that they can be performed in the fastest and most efficient way, finding good solutions to the problem can greatly help improve sectors such as transport and logistics.

Researchers from the ̽��ֱ�� of Cambridge have developed a hybrid, data-driven approach to the problem that not only produces high-quality solutions, but at a faster rate than other state-of-the-art approaches. Their results are presented this week at the International Conference on Learning Representations.

“ ̽��ֱ��importance of global logistics system was brought home to us during the pandemic,” said Dr Amanda Prorok from Cambridge’s Department of Computer Science and Technology, who led the research. “We’re highly reliant on this kind of infrastructure to be more efficient – and our solution could help with that as it targets both in-warehouse logistics, such as the routing of robots around a warehouse to collect goods for delivery, and those outside it, such as the routing of goods to people.”

̽��ֱ��Travelling Salesperson Problem involves a notional delivery driver who must call at a set number of cities – say, 20, 50 or 100 – that are connected by highways all in one journey. ̽��ֱ��challenge is to find the shortest possible route that calls at each destination once and to find it quickly.

“There are two key components to the problem. We want to order the stops, and we also want to know the cost, in time or distance, of going from one stop to another in that order,” said Prorok.

Twenty years ago the route from the warehouse to the destinations might have been fixed in advance. But with today’s availability of real-time traffic information, and the ability to send messages to the driver to add or remove delivery locations on the fly, the route may now change during the journey. But minimising its length or duration still remains key.

There’s often a cost attributed to waiting for an optimal solution or hard deadlines at which decisions must be taken. For example, the driver cannot wait for a new solution to be computed – they may miss their deliveries, or the traffic conditions may change again.

And that is why there is a need for general, anytime combinatorial optimisation algorithms that produce high-quality solutions under restricted computation time.

̽��ֱ��Cambridge-developed hybrid approach does this by combining a machine learning model that provides information about what the previous best routes have been, and a ‘metaheuristic’ tool that uses this information to assemble the new route.

“We want to find the good solutions faster,” said Ben Hudson, the paper’s first author. “If I’m a driver for a courier firm I have to decide what my next destination is going to be as I’m driving. I can’t afford to wait for a better solution. So that’s why in our research we focused on the trade-off between the computational time needed and the quality of the solution we got.”

To do this, Hudson came up with a Guided Local Search algorithm that could differentiate routes from one city to another that would be costly – in time or distance – from routes that would be less costly to include in the journey. This enabled the researchers to identify high-quality, rather than optimal, solutions quickly.

They did this by using a measure of what they call the ‘global regret’ – the cost of enforcing one decision relative to the cost of an optimal solution – of each city-to-city route in the Guided Local Search algorithm. They used machine learning to come up with an approximation of this ‘regret’.

“We already know the correct solution to a set of these problems,” said Hudson. “So we used some machine learning techniques to try and learn from those solutions. Based on that, we try to learn for a new problem – for a new set of cities in different locations – which paths between the cities are promising.

“When we have this information, it then feeds into the next part of the algorithm – the part that actually draws the routes. It uses that extra information about what the good paths may be to build a good solution much more quickly than it could have done otherwise.”

̽��ֱ��results they came up with were impressive. Their experiments demonstrated that the hybrid, data-driven approach converges to optimal solutions at a faster rate than three recent learning-based approaches for the Travelling Salesperson Problem.

In particular, when trying to solve the problem when it had a 100-city route, the Cambridge method reduced the mean optimality gap from 1.534% to 0.705%, a two-fold improvement. When generalising from the 20-city problem route to the 100-city problem route, the method reduced the optimality gap from 18.845% to 2.622%, a seven-fold improvement.

“A lot of logistics companies are using routing methods in real life,” said Hudson. “Our goal with this research is to improve such methods so that they produce better solutions – solutions that result in lower distances being travelled and therefore lower carbon emissions and reduced impact on the environment.”

Amanda Prorok is a Fellow of Pembroke College, Cambridge.

Reference:
Benjamin Hudson et al. ‘Graph Neural Network Guided Local Search for the Traveling Salesperson Problem.’ Paper presented at the International Conference on Learning Representations: https://iclr.cc/virtual/2022/calendar.

A new approach to solving the Travelling Salesperson Problem – one of the most difficult questions in computer science – significantly outperforms current approaches.

We’re highly reliant on this kind of infrastructure to be more efficient – and our solution could help with that

Amanda Prorok

Luis Alvarez

Courier checking parcel for delivery

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Ely’s new cathedral (of books) opens for business

sjr81 — Wed, 27 Jun 2018 08:07:29 +0000

Research recommends how to tackle spread of HIV/AIDS by African truckers

sj387 — Tue, 15 Oct 2013 12:00:00 +0000

Long-distance truck drivers have long-been identified as the primary dispersers of HIV in Sub-Saharan Africa. Truck drivers lead difficult lives with frequent overnight stays away from home, fewer social controls and excessive waiting periods in ports and border crossings, where the availability of commercial sex increases their vulnerability to infectious diseases and other health problems.

Multinational companies predominately outsource their transport supplier to international or local operators as part of their Sub-Saharan supply chain to save cost. Yet, according to a 2006 baseline report on business and HIV/AIDS by GBCHealth, the transport industry ranked last in their efforts to protect their employees against HIV and other infectious diseases.

Now, an investigation of organisational awareness of the risks of HIV transmission within the transport supply chains of Dutch multinational enterprises has resulted in a series of recommendations to help combat the spread of HIV/AIDS. These include companies providing more, and better, HIV/AIDS education, and them seeing HIV/AIDS as an HR priority.

Dr Rodney Irwin, who carried out the research as part of the Master of Studies in Sustainability Leadership at the Cambridge Programme for Sustainability Leadership, said: “There is no cure for HIV but it has become a manageable illness with the global incidence of AIDS declining but they are still major issues for the transport sector. ̽��ֱ��Millennium Development Goals have made significant progress at a macro level but this vulnerable group remain primary victims and vectors of the virus. This research aspires to spur action in Dutch businesses to step up to the issue in their supply chains and offer as much intervention as is possible.”

Irwin’s study focused on 11 Dutch multinational companies that conducted business in southern Africa. Although Dutch multinationals are three times more likely now to advocate a global HIV policy for their supply chain and associates, many of the findings speak of a decrease in the multinationals’ efforts to stem the transmission of this disease. Despite 80% of the Dutch companies having identified HIV/AIDS as an issue, the study found little improvement in the management of HIV/AIDS since the 2006 GBCHealth global survey.

For instance, 36% report having no counselling and testing initiatives in place (15 % in 2006), and 36% provide no access to care, support and treatment services (9% in 2006).

Irwin points to the existence of disagreement between business and government as to who should bear the cost of HIV interventions, as well as the stigma of the disease and prevailing attitudes towards safe sex, HIV testing and other policy actions remaining a strong barrier to tackling the problem. He also suggests that the strong focus on cost-saving as a reason for outsourcing has added to the problem, saying: “Smaller transport companies, who themselves engage in subcontracting, are unable to provide HIV/AIDS interventions if their revenues are eroded by customers seeking costs savings.”

On the basis of his findings, he recommends that companies should support fixed and mobile clinics to provide HIV education, testing and treatment for ‘at risk’ groups such as truck drivers and sex workers. This would open up lines of communication, and impress upon both parties (employer and employee) their own personal responsibilities.

He further recommends that companies should conduct an HIV/AIDS risk assessment not only with direct employees, but also with other stakeholders, especially the transport supply chain. It should also be followed up by a workplace HIV/AIDS policy.

“It’s important to adopt a human capital approach that places a high value on employees, including outsourced and sub-contracted labour,” he said. “HIV/AIDS should be a priority for human resources, rather than a function of corporate social responsibility.”

Finally, he recommends that border crossings must be made more efficient in order to minimise nights away from home for truck drivers, and the encouragement of truck drivers to have their spouses accompany them on long trips where possible.

Irwin hopes that his recommendations will be taken up by companies in order to tackle an escalating problem. Today long-distance truck drivers have an HIV infection rate believed to be at least twice that of the general population in Sub-Saharan Africa. In South Africa, a 2001 study found that 56 per cent of long-distance truck drivers were HIV positive, with 95 per cent of those tested at one truck stop infected. In Malawi, another study concluded that AIDS-related illnesses were truck drivers’ primary killer, above malaria and road traffic accidents.

“HIV and sex are inseparable. Taking about sex is not something you often do in the board room but for transport companies and their users this taboo subject urgently needs to be on the agenda,” he added. “HIV and AIDS are occupational illnesses for the transport sector. I urge these companies and their customers to acknowledge their responsibility. Just as the UK’s HIV awareness campaign in the 1980’s said “Don’t die of Ignorance”, transport companies should step up, confront the stigma and not allow this vulnerable group to die of ignorance.”

Rodney Irwin’s research was carried out as part of a Master of Studies in Sustainability Leadership at the Cambridge Programme for Sustainability Leadership. www.cpsl.cam.ac.uk/Accredited-Programmes

An investigation into how the transport suppliers employed by multinational companies contributes to the spread of HIV in Sub-Saharan Africa urges companies to take action.

HIV/AIDS should be a priority for human resources, rather than a function of corporate social responsibility

Rodney Irwin

Lotte Vermeij

Truck stop

Insights from truck driver Charles Makomba

Charles Makomba is a long-distance truck driver. Talking to Northstar Alliance, a group of NGOs committed to delivering health services throughout Africa, he commented on the problems caused by the long waits for customs clearance.

“It’s a difficult journey because of the problems at the border. There is too much congestion and they are too slow to process our papers. Recently I waited for six days.

“Usually I get a girlfriend, and the following day maybe another girlfriend. It’s high risk because of this dangerous disease. I always use a condom because I’m aware of this disease. Except with my wife, I use condoms every time.

“I don’t think all truck drivers are the same. Some of them are reckless maybe if they’ve got that disease. ̽��ֱ��trucking companies encourage us to use condoms, because they are losing many drivers and it is hard to replace them."

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