diff --git a/.gitignore b/.gitignore index f95245f..ef0c9d0 100644 --- a/.gitignore +++ b/.gitignore @@ -7,6 +7,8 @@ *.pdf *.synctex.gz +*.out +*.toc *.nav *.snm diff --git a/talk/talk.tex b/talk/talk.tex index bf9fa4f..135211a 100644 --- a/talk/talk.tex +++ b/talk/talk.tex @@ -58,8 +58,8 @@ \frametitle{Computational Aspects of PB} \begin{itemize} \item Discrete or continuous projects? + \item How do we model preferences mathematically? \item How do we adequately capture voter's preferences? - \item How do we model these preferences? \item How do we aggregate votes? \end{itemize} \end{frame} @@ -79,12 +79,6 @@ \item A cap for each project is defined \item Fractional funding \end{itemize} - \begin{block}{Bounded Divisible PB} - Each project has a cap $q_p = 1$ and $x_p = [0,1]$ denotes the - fraction of project $p\in P$ that is completed. The set of - feasible budget allocations under a budget $B = 1$ is therefore defined as - \[ \{ \vec{x} : \sum_{p\in P}{x_p}\leq 1 \}. \] - \end{block} \begin{exampleblock}{Example} A project that seeks to donate a bounded amount of money to a charity. @@ -97,33 +91,252 @@ \item Projects are divisible \item No caps for projects \item Generalizable to \emph{Portioning} - \item In practice still bounded by total budget \end{itemize} - \begin{block}{Unbounded Divisible PB} - + \begin{block}{Unbounded Divisible PB} $x_p = [0,1]$ denotes the + fraction of project $p\in P$ that is completed and $c_p(x_p) = + x_p$ is the cost function of project $p$. The set of feasible + budget allocations under a budget $B = 1$ is therefore defined + as \[ \{ \vec{x} : \sum_{p\in P}{x_p}\leq 1 \}. \] + \end{block} + \begin{exampleblock}{Example} + A project that seeks to donate an unbounded amount of money to a + charity. Every additional amount can be used effectively. + \end{exampleblock} +\end{frame} + +\begin{frame} + \frametitle{Bounded Discrete PB} + \begin{itemize} + \item Projects are either fully implemented or not at all + \item Degree of completion has a cap + \item Budget is defined as subset of projects which can be + implemented subject to budget constraints + \end{itemize} + \begin{exampleblock}{Example} + A project for building a new school. + \end{exampleblock} +\end{frame} + +\begin{frame} + \frametitle{Unbounded Discrete PB} + \begin{itemize} + \item Multiple degrees of completion + \item Substages of projects (milestones) can be defined + \item Still bounded by total available budget + \end{itemize} + \begin{exampleblock}{Example} + A project for building public toilets. The degree of completion + is the number of toilets that have already been built. + \end{exampleblock} +\end{frame} + +\section{Preference Modeling} + +\begin{frame} + \frametitle{Preference Modeling} + Model preferences as a cardinal utility function or an ordinal + preference relation: + \begin{block}{Cardinal utility function} + Each resident $i$ has a cardinal utility function $u_i : + A\rightarrow \mathbb{R}$, where $A$ is the set of feasible + allocations. + \end{block} + \begin{block}{Ordinal preference relation} + $\succ_i$ over $A$ + \end{block} + \begin{alertblock}{Problem} + This does not adequately reflect any structural properties of + residents' preferences. + \end{alertblock} +\end{frame} + +\begin{frame} + \frametitle{Preference Modeling} + \begin{itemize} + \item Impose a structural assumption on the utility function: + \[ u_i : 2^P\rightarrow\mathbb{R} \] + and $u_i$ satisfies subadditivity or superadditivity. + \item Use spatial models where preferences are situated in a + metric space and the distance between them models a + resident's utility for another allocation. + \item Take preferences over projects and use a rule to extend + them to allocations. + \end{itemize} +\end{frame} + +\begin{frame} + \frametitle{Cardinal extensions} + \begin{block}{Scalar separable utility function} + A resident $i$ derives utility $u_{i,p}\cdot f_p(x_p)$ from each + project. A resident's utility for an allocation $\vec{x}$ is + additive across projects: + \[ u_i(\vec{x}) = \sum_{p\in P}{u_{i,p}\cdot f_p(x_p)} \] + \end{block} + \begin{block}{Dichotomous preferences} + Assuming $x_p\in\{0,1\}$ and $u_{i,p}\in\{0,1\}$, residents + either approve or disapprove a project and care only about the + number of projects implemented. + \end{block} + \begin{block}{Max set extension} + Utility of an allocation is defined as the utility for a + resident's most favorite project: $u_i(S) = \mathsf{max}_{p\in + S}u_{i,p}$ for each $S\subseteq P$. + \end{block} +\end{frame} + +\begin{frame} + \frametitle{Ordinal extensions} + \begin{block}{Stochastic dominance extension} + For two allocations $\vec{x},\vec{y}\in A$ and + $E_i^1,\dots,E_i^{k_i}$ being the equivalence classes of the + relation $\succ_i$ in decreasing order of preferences: \[ + \vec{x}\succ_{i}^{SD}\vec{y} \text{ iff } + \sum_{j=1}^{l}{\sum_{p\in E_i^j}{x_p}}\geq\sum_{j=1}^{l}{\sum_{p\in +E_i^j}{y_p}}\quad\text{for all } l\in\{1,\dots,k_i\}\] + \end{block} + \begin{block}{Lexicographic extension $\succ_i^{lex}$} + A resident $i$ cares significantly more about project $p$ than + about $p'$ whenever $p\succ_i p'$. + \end{block} + \begin{block}{Scoring rules} + Convert ordinal to cardinal preferences by taking a ranking + $\succ_i$ over projects and determining the utility as $u_{i,p} + = s_k$ where $k$ is the rank in a scoring vector $\vec{s} = + (s_1,\dots,s_m)$ and $s_1\geq\dots\geq s_m\geq 0$. \end{block} \end{frame} \section{Preference Elicitation} -\section{Preference Modeling} +\begin{frame} + \frametitle{Preference elicitation} + \begin{itemize} + \item Also known as \emph{Ballot Design} + \item Communicating full preferences over sometimes + exponentially many allocations is difficult + \item Cognitive burden can lead to lower turnout rates + \end{itemize} +\end{frame} + +\begin{frame} + \frametitle{Preference elicitation} + \begin{block}{Range voting} + Voters rate projects based on their utility for each project. + \end{block} + \begin{block}{$k$-Approval} + Voters approve the $k$ projects they like the most. + \end{block} + \begin{block}{Approval voting} + Voters approve all projects that they like. + \end{block} + \begin{block}{Threshold approval voting} + Voters approve projects where their utility is above a specified + threshold. + \end{block} + \begin{block}{Knapsack voting} + Voters provide ideal allocation based on their preferences. + \end{block} +\end{frame} \section{Vote Aggregation} \begin{frame} - \frametitle{Algorithm Axioms} + \frametitle{Vote Aggregation} \begin{itemize} - \item Pareto Optimality - \item Monotonicity - \item Truthfulness - \item Fairness + \item Voters' preferences are aggregated to determine which + projects to fund + \item Main interest for research + \item Three different approaches: + \begin{itemize} + \item Welfare Maximization + \item Use of Axioms + \item Notions of Fairness + \end{itemize} \end{itemize} \end{frame} -\section{Algorithms} +\begin{frame} + \frametitle{Welfare Maximization} + \begin{block}{Utilitarian Welfare} + The utilitarian welfare of an allocation is the sum of utilities it gives to + residents: + \[ UW(\vec{x}) = + \sum_{i\in N}{u_i(\vec{x})}\text{ for }\vec{x}\in A \] + \end{block} + \begin{block}{Egalitarian Welfare} + The egalitarian welfare of an allocation is the minimum utility + it gives to any resident: + \[ EW(\vec{x}) = + \mathsf{min}_{i\in N}{u_i(\vec{x})}\text{ for + }\vec{x}\in A \] + \end{block} + \begin{block}{Nash Welfare} + The Nash welfare of an allocation is the product of utilities it gives to + residents: + \[ NW(\vec{x}) = + \prod_{i\in N}{u_i(\vec{x})}\text{ for }\vec{x}\in A \] + \end{block} +\end{frame} -\section{Comparison} +\begin{frame} + \frametitle{Use of Axioms} + \begin{block}{Exhaustiveness} + A feasible allocation $\vec{x}$ is called exhaustive if an + outcome $\vec{y}$ is not feasible whenever $y_p\geq x_p$ for all + projects $p$ and a strict inequality holds for at least one + project. + \end{block} + \begin{block}{Discount Monotonicity} + Project $p$'s cost function $c_p$ is revised to $c_p'(x_p)\leq + c_p(x_p)$ after a vote aggregation rule outputs allocation + $\vec{x}$. For the resulting allocation $\vec{y}$, $y_p\geq + x_p$ holds. + \end{block} + \begin{block}{Pareto Optimality} + An allocation $\vec{x}\in A$ Pareto dominates another allocation + $\vec{y}\in A$ if $u_i(\vec{x})\geq u_i(\vec{y})$ for all $i\in + N$ and $u_i(\vec{x}) > u_i(\vec{y})$ for some $i\in N$. An + allocation $\vec{z}\in A$ is optimal if no allocation dominates + it. + \end{block} +\end{frame} -\section{Practicality} +\begin{frame} + \frametitle{Notion of Fairness} + \begin{block}{The Core of PB} + An allocation $\vec{x} \in A$ is a core solution if there is no + subset $S$ of voters who, given a budget of $(|S|/n)B$, could + compute an allocation $\vec{y}\in A$ such that every voter in + $S$ receives strictly more utility in $\vec{y}$ than in + $\vec{x}$. + \end{block} + \begin{block}{Proportionality} + An allocation $\vec{x}$ should be proportionally reflected by + the division of voters. A majority of voters should have a + majority of the budget under their control but a minority should + have a minority of the budget under their control. + \end{block} +\end{frame} + +\section{Future Directions} + +\begin{frame} + \frametitle{Future Areas of Interest} + \begin{itemize} + \item Multi-dimensional constraints + \item Hybrid models + \item Complex resident preferences + \item Market-based approaches + \item The role of information + \item Research spanning the entire PB process + \end{itemize} +\end{frame} + +\begin{frame} + \centering + \Large + Thank you for your attention! \\ + Questions \& Answers +\end{frame} \end{document} diff --git a/talk/taxonomy.png b/talk/taxonomy.png index bb217ce..bb9ee82 100644 Binary files a/talk/taxonomy.png and b/talk/taxonomy.png differ