On dynamic aggregation systems
N. L. Polyakov,
M. V. Shamolin
Abstract:
We consider consecutive aggregation procedures for individual preferences
$\mathfrak c\in \mathfrak C_r(A)$ on a set of alternatives
$A$,
$|A|\geq 3$: on each step, the participants are subject to intermediate collective decisions on some subsets
$B$ of the set
$A$ and transform their a priori preferences according to an adaptation function
$\mathcal{A}$. The sequence of intermediate decisions is determined by a lot
$J$, i.e., an increasing (with respect to inclusion) sequence of subsets
$B$ of the set of alternatives. An explicit classification is given for the clones of local aggregation functions, each clone consisting of all aggregation functions that dynamically preserve a symmetric set
$\mathfrak D\subseteq \mathfrak C_r(A)$ with respect to a symmetric set of lots
$\mathcal{J}$. On the basis of this classification, it is shown that a clone
$\mathcal{F}$ of local aggregation functions that preserves the set
$\mathfrak{R}_2(A)$ of rational preferences with respect to a symmetric set
$\mathcal{J}$ contains nondictatorial aggregation functions if and only if
$\mathcal{J}$ is a set of maximal lots, in which case the clone
$\mathcal{F}$ is generated by the majority function. On the basis of each local aggregation function
$f$, lot
$J$, and an adaptation function
$\mathcal{A}$, one constructs a nonlocal (in general) aggregation function
$f_{J,A}$ that imitates a consecutive aggregation procesure. If
$f$ dynamically preserves a set
$\mathfrak D\subseteq \mathfrak C_r(A)$ with respect to a set of lots
$\mathcal{J}$, then the aggregation function
$f_{J,A}$ preserves the set
$\mathfrak{D}$ for each lot
$J\in\mathcal{J}$. If
$\mathfrak D=\mathfrak R_2(A)$, then the adaptation function can be chosen in such a way that in any profile
$\mathbf c\in (\mathfrak R_2(A))^n$, the Condorcet winner (if it exists) would coincide with the maximal element with respect to the preferences
$f_{J, \mathcal A}(\mathbf c)$ for each maximal lot
$J$ and
$f$ that dynamically preserves the set of rational preferences with respect to the set of maximal lots.
UDC:
510.6+
510.633