Archive for bee

bees at work

Posted in Kids, pictures with tags , , , , , on September 13, 2015 by xi'an

efficient learning in ABC

Posted in Statistics with tags , , , , , , on October 11, 2012 by xi'an

Jean-Michel Marin just posted on arXiv a joint paper of ours, Efficient learning in ABC algorithms. This paper, to which elaboration [if not redaction] I contributed to, is one of the chapters of Mohammed Sedki’s thesis. (Mohammed is about to defend this thesis, currently with reviewers. A preliminary version of this paper was presented at ABC in London and it is in revision with Statistics and Computing. Hence missing the special issue!)

The paper builds on the sequential ABC scheme of Del Moral et al. (2012), already discussed in this post, where the tolerance level at each step is adapted from the previous iterations as a quantile of the distances. (The quantile level is based on a current effective sample size.) In a “systematic” step, the particles that are closest to the observations are preserved and duplicated, while those farther away are sampled randomly. The resulting population of particles is then perturbed by an adaptive (random walk) kernel and the algorithm stops when the tolerance level does not decrease any longer or when the acceptance rate of the Metropolis step is too low. Pierre Pudlo and Mohammed Sedki experimented a parallel implementation of the algorithm, with an almost linear improvement in the number of cores. It is less clear the same would work on a GPU because of the communication requirements. Overall, the new algorithm brings a significant improvement in computing time when compared with earlier versions, mainly because the number of simulations from the model is minimised. (It was tested on a rather complex population scenario retracing the invasion of honeybees in Europe (in connection with the previous post!)

bees in action

Posted in pictures with tags , , , , on October 7, 2012 by xi'an

a passiflora visitor

Posted in pictures with tags , , on September 6, 2012 by xi'an

Insect collection [live]

Posted in Kids, pictures with tags , , , on May 24, 2010 by xi'an

The Museum d’Histoire Naturelle has launched a large survey of pollen gathering insects all over France and asks volunteers to contribute their observations according to a rather simple protocol. (Well, not that simple: I tried to upload my series of pictures of the lilac tree at the back of my garden and failed…) I do not know how representative the data thus gathered will be nor how the biologists in charge of the study are going to use it but this is a neat idea nonetheless…