Monday, 29 November 2010

Supply chain benefits

Over the last few years, O.R. professionals have given a great deal of attention to supply chains and their behaviour. O.R. people have improved JIT systems, developed algorithms for distribution of goods, and much else. In Saturday's Indepenedent newspaper (27/Nov/2010, page 55) there was an amusing story of the consequences of improving supply chains.

The story reads: "The John Lewis quest for worldwide domination continues with another new initiative designed to ensure shoppers never leave their department stores. Retail Week reports that supply chain improvements have reduced the amount of space John Lewis needs for stockrooms these days, so it plans to turn some of them into beauty spas and hairdressers. It's even promising to install theatrical stages in some of its cafes so you can be entertained while taking a break from spending your money."

Retail Week had the original story in its issue dated 26th November.

The lesson for O.R. models of supply chains is that they need to consider what happens to storeroom space when the needs for buffer stock is reduced. These aspects of the system may not appear automatically in the supply chain model ... but evidently they should!

Monday, 15 November 2010

Parking meter risk

In the street where I live, there are parking restrictions, so if you park on weekdays between 9:30am and 3:3opm, you must pay. The days and the times are to deter people from parking and catching a bus into Exeter, since the maximum length of stay is 4 hours. This means that there are three parking meters in the street. About once a week, a couple of men in a van come round to collect the cash from the machines.

Come to another city, Portsmouth, where my work has taken me, and there the parking meters in the streets that I use are labelled "No cash is left in this machine overnight". A similar notice applies in the "pay and display" car parks in the city centre of Exeter.

So we have different policies concerning the collection of cash. I doubt whether anyone constructed a model to determine the policy for our street and the different one for the second category. It could be an interesting model to work with. Balance the cost of collection, the amount expected to be collected, with the cost of a machine, the perceived risk of vandalism and robbery from a machine, etc.

Qantas rescheduling

After a recent "incident" in which an A380 airbus had to abort its flight, all the company's wide-bodied jets have been withdrawn. How does an airline deal with the the knock-on effect of this? They reschedule their flights and passengers. And, we, the public, see the results. Rescheduling has involved the downsizing of aircraft across all Qantas international routes.

Flagship routes to Los Angeles and London from Australia, usually operated by the super-jumbos, will now use older and smaller Boeing 747s, as will all other A380 flights. 100 passengers per flight who were bumped off have been transferred to other airlines.

The downsizing of shorter flights will continue with Boeing 747 flights to Hong Kong and Tokyo now using Airbus 330s, replaced on their normal routes such as Singapore to Perth with even older Boeing 767s. According to the airline, although it is committed to bringing its A380s back into service as early as possible, the new schedules give certainty to those travelling in the near future.

As the Qantas grounding drags on, fares on certain routes have been increased.

That's the public picture; behind this there must have been some complex modelling, which will be kept restricted. Maybe one day, some Qantas O.R. worker will tell us about the models that were hastily built and modified. If you have been involved with a large O.R. problem, then you can imagine what is involved. To replace aircraft A on flight A1 means substituting aircraft B. How many passengers will be lost? What will it cost? But aircraft B was assigned to flight B1 and needs to have a substitute, aircraft C. And so on. Then, the speeds of A, B and C are likely to be different, so there are further consequences.

Which passengers should be bumped? There will be data on the flying habits of the passengers, which can be used to help this. I suspect that the O.R. people at Qantas are busy doing their hidden science!

Friday, 5 November 2010

The greatest invention for queues

Twice, in the last month, I have been caught in unorganised multiserver queues. In one, long lines formed for each server, and people at the back jockeyed as they watched thelines move. Those in the middle simply were stuck in the queue they had selected.

In the other, people milled around until there was a free server, and by mutual agreement identified the leading person in the line.

Both queues could have been improved by the use of snake barriers, as used in theme parks and at many airports (but not in Madeira, the first place I noted). Surely these are one of the great inventions of queue management?

Perception of value

The Commissioner for Victims of Crime Louise Casey has called for the right to trial by jury to be stopped for everything other than major crimes such as rape and murder. Casey said: "Defendants should not have the right to choose to be tried by a jury over something such as the theft of a bicycle or stealing from a parking meter."

How valuable is a bicycle? Louise Casey obviously thinks that they are cheap, that cycle crime is minor and trivial. But, has she bought a bike recently? Bikes cost a lot more than the money you can get out of a parking meter, with many worth over £1000, more than some cars. Moreover, organised criminal gangs are responsible for stealing thousands of pounds worth of bikes: for their victims, this is not a trivial matter. According to the British Crime Survey, 480,000 bikes are stolen every year.

(Some of the above has come from the Cyclist's Touring Club ( For O.R. scientists, her misconception is a warning; make sure that everyone knows (or agrees) the real value of items in your studies. The classic area is placing a value on the cost of inventory. How much does it cost to store one widget for one time period?

How big a sample? Follow up.

The results of my sample (blog of October 25 2010) came back this week, and they show no trace of cancer. Thank God!

However, in these days of customised lettters, it was sad to see that the NHS could not use their data in a friendly way. Part of the letter applied to follow-up tests, which happen every two years between the age of 60 and 75 (don't ask how "every two years" fits into a fifteen year period) and then are optional. It is not too difficult to customise the letter to say either "We will invite you to a test in two years time" or "You have reached the age when testing becomes optional".