Caen snapshot

new camera (stills)

Toulouse snapshot (#3)

Saigon snapshots

I did not have too much time to explore Saigon and even less Vietnam in the 62 hours I spent there, especially with the course and the conference, but I very much enjoyed the feeling. From riding on the back of  a motorbike in the traffic (thanks to a guest student!) to having pho in a simple restaurant by the side of the street, from watching improbable loads going by on the same motorbikes to wandering in the shops around, to talking with students around the course, my snapshots all came back in the best possible light and I found my stress about food safety, street security, pollution, &tc., very quickly fading away and I wish my suitcase would have arrived in time so that I could have gone jogging in the vicinity of my hotel (rather than using the treadmill in the hotel). I have obviously seen nothing of the countryside and wish I can go back there in the future.

This most kind student also took me to the War Remnants Museum, which is a highly sobering place about the destruction and long-term health consequences of the Vietnam War, in particular the generations of victims of the Agent Orange sprays… Even when accounting for the (mild) propaganda bias. Actually, a few days prior to flying to Vietnam, I had read Bao Ninh’ Sorrow of War, a moving and very grim account of the war and of the after-war from a disillusioned soldier.  (The book was banned in Vietnam for a while. And thus I was unsure I could travel with it…)

ABC in Roma (#2)

Just a few more words written on my return home from Roma (on an uneventful and sunny trip). On a personal side (that readers can skip!), it was a pleasure as always to be two days in Roma, from running in the early morning, beating the rain and the traffic (and with no map nor camera!) and finding new routes, one on the banks of Tevere and another one along the city walls, to meeting old friends over a plate of pasta, to buying fresh bread and market fruits in the early morning, to enjoying the beauty of La Città Eterna… Too short a trip obviously, but this was/is a busy week!

On the academic side, as mentioned yesterday, the program was quite in tune with my lines of research on ABC and I though a (wee) bit harder about the solutions proposed by the various speakers. One clear tendency is the idea of borrowing from pseudo- or simplified models, either to build estimates (as in indirect inference) or to run the simulation and the calibration (as in, e.g., Olli’s work). As remarked by Judith Rousseau after my talk, we may even have to move further when facing complex models, namely when the simulation of pseudo-samples gets too overwhelming. The issue is then on keeping a connection with the “true” model.

Another theme that crossed several talks is the tension between particle methods (incl. pMCMC) and ABC methods in dynamical models since they usually both apply in such cases. Darren Wilkinson’s talk (that I alas missed in order to catch my plane but recovered by email at the airport, soon to be on-line) did address this opposition, concluding in favour of ABC for the Lotka-Volterra system… My vague feeling is that ABC solutions could indeed come above when they do not rely on the hidden (Markov) structure, in the sense that they do not aim at simulating a joint distribution involving this latent structure…