Wednesday, August 27, 2014

Markov Chains Monte Carlo, Oh my!

Yesterday was the craziness we call Librarypalooza. We set up tables on the first floor explaining various library services from printing help to employment opportunities to research appointments. And then in exchange for visiting two or more of our tables we bribe the students with a cookout on the plaza in front of the Library. I was on the crowd control team guiding students and handing out passports to prove they had visited at least two tables. I didn't do much crowd control.

The research sent students to find me. Oh, your majoring in Science - we have a librarian who can help you with that. He's out in the lobby. I spent a good amount of time giving on the fly "How to use the library for Science research" and making research appointments for later in the week. And handing out my business cards.

One statistics student cornered me. He has an interesting problem. He is working on a work study project and needs to do some economic modeling. We briefly discussed various models he could use and MCMC came up. I had mentioned Monte Carlo methods, since I'm looking at them to model a demand driven acquisition (DDA) program. He couldn't remember what the other MC in MCMC stood for and commented it was an advance method. I thought nothing of it until I got in the shower this morning.

I was thinking about DDA and how my curve fit model was giving me good predictions - the experience in the last quarter seem to indicate the model overstates the number of books being purchased. I've been thinking about how to use Monte Carlo methods and it hit me - I have a Markov Chain. Using a physical analogy, think of each title as having a "state", there is a certain probability will flip to the next state. This sequence of states is the Markov Chain. It's a rather complex system - I think of it as a series of phase transitions - from available for rent to either owned or out of the catalog/no longer available.

So one of today's projects will be translating the model into a spreadsheet and see if predictions match reality. I am in over my head. Just keep swimming. Just keep swimming.

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