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diff --git a/paper/sections/introduction.tex b/paper/sections/introduction.tex new file mode 100644 index 0000000..6eda59d --- /dev/null +++ b/paper/sections/introduction.tex @@ -0,0 +1,54 @@ +The natural “diminishing return” property of submodular functions makes them +suitable to model many real-life scenarios. However, even when they are +suitable as a model, it is not realistic to assume that they are entirely +known. For example, most submodular functions depend on unknown parameters that +have to be learned from observations. + +A recent line of work has focused on learning submodular functions. The +PMAC-learnable framework formalizes what it means to learn a submodular +function in an “overall” sense. For specific examples of submodular functions, +results are known on how well the parameters of the function can be learned +from observations. + +When the experimenter wishes to optimize the unknown submodular function, the +well-known approximation algorithms cannot be readily applied because they rely +on a value query oracle, which is much stronger than what the present scenario +suggests (at best, random independent samples). The results on learning +submodular functions also seem to be insufficient in that they are myopic to +the ultimate use which will be made of the submodular function (optimizing). +The experimenter experimenter only cares about learning the function to the +extent that what he knows is sufficient to optimize it. As such, the main +question underlying the present work is the following: + +\begin{center} + \emph{What is a good model of learning for submodular functions when the + ultimate goal is to be able to optimize them?} +\end{center} + +We make the following contributions: +\begin{itemize} + \item We show how the PMAC learning framework does not provide a satisfying + framework for optimizing under uncertainty. In particular, we show that + there are functions which are PMAC-learnable but not optimizable and + vice-versa. + \item For specific class of submodular functions, we show how to optimize + them under uncertainty. +\end{itemize} + +\subsection{Related Work} + +\paragraph{Maximizing submodular functions} Vast literature on maximizing +submodular functions under many kind of constraints. All the algorithms rely on +some kind of oracle (e.g. value query or demand query) which is stronger than +what we have: access to polynomially many observations coming from +a distribution. In particular, an algorithm cannot make arbitrary (and +certainly not adaptive) queries to the oracle. + +\paragraph{PMAC-learning} Interesting line of work, but oblivious to the +ultimate goal. + +\paragraph{Bandits} Interesting in that it ties together learning and +optimizing. However, it assumes that arbitrary queries can be made to an oracle +allowing the experimenter to explore more efficiently (even though the standard +regret benchmark means that he will incur some cost for exploring vs +exploiting. |
