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Standard micro-economics concentrate on the description of markets but is seldom interested in production. Several economists discussed the concept of a firm, as opposed to an open labour market where entrepreneurs would recrute workers on the occasion of each business opportunity. Coase \cite{Coase} is one of them, who explains the existence of firms as institution because they reduce the transaction costs with respect to an open labour market. Whatever the rationale proposed by economists to account for the existence of firms, their perspective is based on efficiency and cost analysis. Little attention is paid to the dynamics of emergence and evolution of firms. The aim of the present manuscript is to check the global dynamical properties of a very simple model based on bounded rationality and reinforcement learning. Workers and managers are localised on a lattice and they choose collaborators on the basis of the success of previous work relations. The choice algorithm is largely inspired rom the observation and modeling of long term customer/sellers relationships observed on perishable goods markets discussed in Weisbuch etal\cite{Weisbuch} and Nadal etal\cite{Nadal}. The model presented here is in no way an alternative to Coase. We describe the build-up of long term relationships which do reduce transaction costs, and we deduce the dynamical properties of networks built from our simple assumptions. In conclusion, the present model explains the metastability of employment relations in the firm, but something has to be added to it to explain the more efficient workload repartition observed in real firms., Comment: 13 pages including all figures

The dynamic behavior of cluster algorithms is analyzed in the classical mean field limit. Rigorous analytical results below $T_c$ establish that the dynamic exponent has the value $z_{sw}=1$ for the Swendsen-Wang algorithm and $z_{uw}=0$ for the Wolff algorithm. An efficient Monte Carlo implementation is introduced, adapted for using these algorithms for fully connected graphs. Extensive simulations both above and below $T_c$ demonstrate scaling and evaluate the finite-size scaling function by means of a rather impressive collapse of the data., Comment: Revtex, 9 pages with 7 figures

We present a new measure of the Dynamical Critical behavior: the "Multi-scale Dynamical Exponent (MDE)", Comment: 9 pages,Latex, Request figures from nathanp@vms.huji.ac.il

We describe a method to study the rate at which modes decorrelate in numerical simulations. We study the XY model updated with the Metropolis and Wolff dynamics respectively and compute the rate at which each eigenvector of the dynamics decorrelates. Our method allows us to identify the decorrelation time for each mode separately. We find that the autocorrelation function of the various modes is markedly different for the `local' Metropolis compared to the `non-local' Wolff dynamics. Equipped with this new insight, it may be possible to devise highly efficient algorithms., Comment: 16 pp (LaTeX), PUPT-1378 , IASSNS-HEP-93/2

Computations in Dynamical Triangulation Models of Four-Dimensional Quantum Gravity involve weighted averaging over sets of all distinct triangulations of compact four-dimensional manifolds. In order to be able to perform such computations one needs an algorithm which for any given $N$ and a given compact four-dimensional manifold $M$ constructs all possible triangulations of $M$ with $\leq N$ simplices. Our first result is that such algorithm does not exist. Then we discuss recursion-theoretic limitations of any algorithm designed to perform approximate calculations of sums over all possible triangulations of a compact four-dimensional manifold., Comment: 8 Pages, LaTex, PUPT-1327