# Multivariate Archimax copulas

Our paper, written jointly also with Anne-Laure Fougères, Christian Genest and Johanna Nešlehová, entitled Multivariate Archimax Copulas, should appear some day in the Journal of Multivariate Analysis.

A multivariate extension of the bivariate class of Archimax copulas was recently proposed by Mesiar & Jagr (2013), who asked under which conditions it holds. This paper answers their question and provides a stochastic representation of multivariate Archimax copulas. A few basic properties of these copulas are explored, including their minimum and maximum domains of attraction. Several non-trivial examples of multivariate Archimax copulas are also provided.

In this paper, we extend the class of Archimax copulas, introduced in dimension 2 in Bivariate Distributions with Given Extreme Value Attractor, by Philippe Capéraà, Anne-Laure Fougères and Christian Genest, inspired by some ideas mentioned in a paper published in Kybernetika a few years ago. I will try to post additional material, soon…

# Think academic journals look the same ? Well, some do…

We have seen yesterday that finding an optimal strategy to publish is not that simple. And actually, it can be even more difficult in the case the journal rejects the paper (not because it is not correct, but because “it does not fit” with the standards, the quality of the journal, the audience, the editor’s mood, or whatever). The author has basically two choices,

• forget about the article and move to something else (e.g. start a blog where he/she will be the author and the editor)
• pretend that the article is worth publishing and then try to find another journal with similar interests

But this last choice is not that easy, since sometimes the author think that this journal was indeed the one that should publish it (e.g. all the articles on the subject have been published in that journal).
So I was wondering if there were clusters of journals, i.e. journals that publish almost the same kind of articles (so that next time one of my paper is rejected by the editor, I just go to for some journal in the same cluster).
So what I did is extremely simple: I looked at articles titles and looked for correlations between words frequency (I could have done that in key words, but I am not a big fan of those key words). I looked at 35 journals (that are somehow related to my areas of interest) and looked at titles of all articles published over the last 20 years. Then I kept the top 1000 of words, and I removed standard short words (“a“, “the“, “is“, etc). Actually, my top words looks like

```"models" "model" "data" "estimation" "analysis" "time"
"processes" "risk" "random" "stochastic" "regression"
"market" "approach" "optimal" "based" "information"
"evidence" "linear" "games" "bayesian" "theory" "effects"
"distribution" "multivariate" "tests" "markets" "markov"
"equilibrium" "dynamic" "process" "distributions"
"application" "stock" "likelihood"```

Then, I ran a principal component analysis on my dataset (containing 960 variables – here words – and 35 observations – here journal names).

```library("FactoMineR")
res.pca = PCA(MATRICE, scale.unit=TRUE, ncp=5,
graph=FALSE)
plot.PCA(res.pca, axes=c(1, 2), choix="ind")```

The projection of the journals on the first two axis looks like that

Here, we can clearly observe some clusters : on the up-left Journal of Finance and Journal of Banking and Finance (say financial journals) on the top-right Biometrika, Biometrics, Computational Statistics and Data Analysis and Journal of Econometrics (JASA is not far away, i.e. applied statistics journal). And below, on the right, Stochastic Processes and their Applications, Annals of Applied Probability, Journal of Applied Probability, Annals of Probability, Proceedings of AMS and Topology and Applications (ie more theoretical journal).
Note that the projection is rather robust: if I consider my first 200 words, the graph is the same

In order to go further in the interpretation, we can also plot variables, i.e. words from titles,

where we cannot distinguish anything. So if I just look at my top 30, here they are,

On top left we see market(s), risk or information; on top right analysis, effects, models or tests; while below we see Markov or process(es). And we can observe interesting facts: in finance in statistics, we talk about dynamics while in theoretical (mathematical) journal it is about processes.
But the goal was to find cluster, i.e. classes of journals that publish papers with similar titles.

```DISTANCE = dist(MATRICE)
cah = hclust(DISTANCE)
plot(cah)```

Here we have

If some classes a rather natural (Journal of Applied Proba. and Advances in Applied Proba.or Economic Theory, Journal of Economic Theory and Journal of Mathematical Economics) some strong correlation are not simple to understand, (e.g. Insurance: Mathematics and Economics and Management Science or Annals of Statistics and the Journal of Multivariate Analysis).
Again, it might be possible to spend hours on the graphs, but if I want – someday – to submit something to one of those journals, I guess I have to stop here, and move to something else…