On Relative entropy

Relative entropy is a really cool tool that which haven’t heard of before you are in for a treat! Also known as Kullback-Leibler divergence, it is the measure of the distance between 2 probability distributions [e.g. p(x) and q(x) ]  on a random variable X. It is defined as: Where H(P,Q) is the cross entropy…

Multivariate Gaussian Mixture Model done properly

Michael Betancourt recently wrote a nice case study describing the problems often encountered with gaussian mixture models, specifically the estimation of parameters of a mixture model and identifiability i.e. the problem with labelling mixtures (http://mc-stan.org/documentation/case-studies/identifying_mixture_models.html). Also there has been suggestions that GMM’s can’t be easily done in Stan. I’ve found various examples online of simple…

Best space themed christmas ideas…

Its almost christmas and time to think about christmas presents. Below i list my top 10 christmas presents for the astronomy/space obsessed! 10. Time Travelling Toby and the Apollo moon landing by Graham Jones Graham Jones’ exciting take on the Apollo moon landings, this beautifully illustrated book is the perfect gift for those young kids (1-10)…

Exomars I

In today’s post I want to talk about the Exomars mission, what it’s all about, all the drama in the news and also the future of Exomars. For those that don’t know, ExoMars is joint mission between ESA (European space agency) and ROSCOSMOS (Russian space agency) to search for the evidence of life on Mars.…

Science and games

Over the past year or so, I have been helping a small games company called Atomicom develop a new game. But how does a person like me fit into the gaming world? Well I was given the role of scientific advisor – simple task for a PhD in astrophysics right? think again. JCB Pioneer Mars is a…