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@ -102,8 +102,8 @@ adapts the Stochastic Block Model (SBM)
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to bipartite graphs.
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\textit{Note :}\begin{small}
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Please note that we prefer the term ``BiSBM`` and will use both LBM and BiSBM to
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designate the Stochastic Block Model applied on bipartite networks.
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Please note that we prefer the term \enquote{BiSBM} and will use both LBM and BiSBM to
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designate the Stochastic Block Model adapted to bipartite networks.
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\end{small}
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This model supposes that:
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@ -130,10 +130,11 @@ This model supposes that:
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Parameters
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\begin{itemize}
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\item $\pi_{\bullet} = \mathbb{P}(Z_i = \bullet)$ for rows and $\rho_{\bullet} = \mathbb{P}(W_j = \bullet)$ for columns
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\item $\alpha_{{\color{blueind}\bullet}{\color{burntorange}\bullet}} = \mathbb{P}(X_{ij} = 1 | Z_i = {\color{blueind}\bullet}, W_j = {\color{burntorange}\bullet})$, probability of connectivity knowing node membership blocks.
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\item $\alpha_{{\color{blueind}\bullet}{\color{burntorange}\bullet}} = \mathbb{P}(X_{ij} = 1 | Z_i = {\color{blueind}\bullet}, W_j = {\color{burntorange}\bullet})$, parameter influencing the probability and value of a link knowing node
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membership blocks.
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\end{itemize}
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On \ref{fig:LBMvisu}, $\bm{\pi}$ are the probabilities for a row node to belong
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On figure~\ref{fig:LBMvisu}, $\bm{\pi}$ are the probabilities for a row node to belong
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to the row block of corresponding color, $\bm{\rho}$ are the probabilities for
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a column node to belong to the column block of corresponding color and
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$\bm{\alpha}$ is a matrix $Q_1 \times Q_2$ of the connectivity parameters
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@ -143,20 +144,19 @@ of the network we are referring to this connectivity matrix.
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This model can be used to easily generate bipartite graphs with complex and
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very varied structures. But when trying to determine the structure of a given
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network we need to find those parameters and as the row and column block
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memberships are \emph{latent} i.e.,\ they are not known and must be inferred.
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memberships are \emph{latent} i.e.,\ they are not known, they must be inferred.
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For this a common approach is to use a \emph{variational} EM algorithm (proposed
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For this a common approach is to use a \emph{variational} EM algorithm, proposed
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for SBM in~\cite{daudinMixtureModelRandom2008} and for LBM in
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~\cite{govaertEMAlgorithmBlock2005}) those groups and the required parameters
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~\cite{govaertEMAlgorithmBlock2005}. The groups and required parameters
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can be inferred by maximizing a lower bound of the likelihood.
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\section{colSBM model, a joint model for a collection of networks}
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\label{sec:colsbm-model-a-joint-model-for-a-collection-of-networks}
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The \emph{colSBM} model introduced by ~\cite{chabert-liddellLearningCommonStructures2024a}
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propose an extension of the SBM model to collections of simple (or unipartite)
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networks. A collection is a set of networks which nodes are not common or linked
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between different networks, the interactions have the same valuations and
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are of the same type.
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networks. A collection is a set of networks which nodes are not in common nor
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linked between different networks and the interactions have the same valuations.
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The model can retrieve the shared structure in a collection, indicate if
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networks should be grouped in a collection and in a large pool of networks,
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@ -164,3 +164,5 @@ collections with common structures.
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The next step after designing this collection model for unipartite networks was
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to extend it to the bipartite case.
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% DONE Relu
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