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authorYigit Sever2020-11-07 03:38:07 +0300
committerYigit Sever2020-11-07 03:38:29 +0300
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Polish question 2
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@@ -304,7 +304,7 @@ We have implemented \emph{Gale-Shapley} and an instance set creation script to t
304\section{Stable Matching Variation}% 304\section{Stable Matching Variation}%
305\label{sec:stable_matching_variation} 305\label{sec:stable_matching_variation}
306 306
307% stable matching question ALMOST {{{1 % 307% stable matching question {{{1 %
308 308
309\begin{question} 309\begin{question}
310 Consider a Stable Matching problem with men and women. 310 Consider a Stable Matching problem with men and women.
@@ -313,12 +313,15 @@ We have implemented \emph{Gale-Shapley} and an instance set creation script to t
313 Either give a proof that shows such an improvement is impossible, or give an example preference list for which an improvement for $w$ is possible. 313 Either give a proof that shows such an improvement is impossible, or give an example preference list for which an improvement for $w$ is possible.
314\end{question} 314\end{question}
315 315
316Example preference list for men; $M = {x,y,z}$ and women: $W = {a,b,c}$. 316We will give an example instance.
317Let's take the example preference list for men; $M = {x,y,z}$ and women: $W = {a,b,c}$.
317 318
318\begin{table}[!htb] 319\begin{table}[!htb]
319 \caption{Preference lists of women.} 320 \caption{Preference lists of women}%
321 \label{table:2_general}
320 \begin{minipage}{.5\linewidth} 322 \begin{minipage}{.5\linewidth}
321 \caption{Everyone is being truthful} 323 \caption{Everyone is being truthful}%
324 \label{table:2_true}
322 \centering 325 \centering
323 \begin{tabular}{l|lll} 326 \begin{tabular}{l|lll}
324 \textbf{a} & y & x & z \\ 327 \textbf{a} & y & x & z \\
@@ -328,19 +331,22 @@ Example preference list for men; $M = {x,y,z}$ and women: $W = {a,b,c}$.
328 \end{minipage}% 331 \end{minipage}%
329 \begin{minipage}{.5\linewidth} 332 \begin{minipage}{.5\linewidth}
330 \centering 333 \centering
331 \caption{a is lying about their preference} 334 \caption{a is lying about their preference}%
335 \label{table:2_lie}
332 \begin{tabular}{l|lll} 336 \begin{tabular}{l|lll}
333 \textbf{a} & y & z & x \\ 337 \textbf{a} & y & z & x \\
334 \textbf{b} & x & y & z \\ 338 \textbf{b} & x & y & z \\
335 \textbf{c} & x & y & z 339 \textbf{c} & x & y & z
336 \end{tabular} 340 \end{tabular}
337 \begin{tikzpicture}[overlay] 341 \begin{tikzpicture}[overlay]
338 \draw[red, line width=1pt] (-0.72,0.52) ellipse (0.70cm and 0.2cm); 342 \draw[red, line width=1pt] (-0.72,0.52) ellipse (0.70cm and 0.2cm);
339 \end{tikzpicture} 343 \end{tikzpicture}
340 \end{minipage} 344 \end{minipage}
341\end{table} 345\end{table}
342 346
343% TODO: final polish, highlight the lies <06-11-20, yigit> % 347In the example given above in Table~\ref{table:2_general}, we have two cases for women, Table~\ref{table:2_true} where everyone has given their actual preference list and Table~\ref{table:2_lie} where $a$ has lied about their \nth{2} and \nth{3} preferences.
348
349The following is the men's preference table;
344 350
345\begin{table}[htb] 351\begin{table}[htb]
346 \centering 352 \centering
@@ -353,7 +359,7 @@ Example preference list for men; $M = {x,y,z}$ and women: $W = {a,b,c}$.
353 \label{tab:men_pref} 359 \label{tab:men_pref}
354\end{table} 360\end{table}
355 361
356The trace of \emph{Gale-Shapley} algorithm for the truth telling case; 362The trace of \emph{Gale-Shapley} algorithm for the truth telling case with Table~\ref{table:2_true} and Table~\ref{tab:men_pref} is below;
357 363
358\begin{enumerate} 364\begin{enumerate}
359 \item Matching x with a (a) 365 \item Matching x with a (a)
@@ -363,30 +369,36 @@ The trace of \emph{Gale-Shapley} algorithm for the truth telling case;
363 \item Matching z with c (a) 369 \item Matching z with c (a)
364\end{enumerate} 370\end{enumerate}
365 371
372Which produces the following matching. Note that $a$ is matched with their \nth{2} choice.
373
366\begin{align*} 374\begin{align*}
367 x &\rightarrow a \\ 375 x &\rightarrow a \\
368 y &\rightarrow b \\ 376 y &\rightarrow b \\
369 z &\rightarrow c 377 z &\rightarrow c
370\end{align*} 378\end{align*}
371 379
372The trace of \emph{Gale-Shapley} algorithm when \emph{a} lies about their preferences; 380Now let's examine the trace of the algorithm when $a$ lies by providing an altered preference table. The trace below uses Table~\ref{table:2_lie} and Table~\ref{tab:men_pref};
373 381
374\begin{enumerate} 382\begin{enumerate}
375 \item Matching y with b (a) 383 \item Matching y with b (a)
376 \item Matching z with a (a) 384 \item Matching z with a (a)
377 \item x proposes to a but gets rejected because a prefers z more (c) 385 \item \textbf{x proposes to a but gets rejected because a lies by saying that they like z more (c)}
378 \item Matching x with b, y is now free (b) 386 \item Matching x with b, y is now free (b)
379 \item Matching y with a, z is now free (b) 387 \item \textbf{Matching y with a, z is now free (b)}
380 \item z proposes to b but gets rejected because b prefers x more (c) 388 \item z proposes to b but gets rejected because b prefers x more (c)
381 \item Matching z with c (a) 389 \item Matching z with c (a)
382\end{enumerate} 390\end{enumerate}
383 391
392The highlighted lines show that $a$ lies when proposed by $x$ and then is able to trade up to $y$. The following it the final matching;
393
384\begin{align*} 394\begin{align*}
385 x &\rightarrow b \\ 395 x &\rightarrow b \\
386 y &\rightarrow a \\ 396 y &\rightarrow a \\
387 z &\rightarrow c 397 z &\rightarrow c
388\end{align*} 398\end{align*}
389 399
400Woman $a$ was able to get their highest preferred option $y$ by telling a lie. We have proved that an improvement is possible.
401
390% 1}}} % 402% 1}}} %
391 403
392\section{Asymptotics}% 404\section{Asymptotics}%