diff --git a/main.tex b/main.tex index 1d4bc018e03f8c82385b8846c011551f767ef34c..e456eadc90bc86d369595262e0b9ff098103ba06 100644 --- a/main.tex +++ b/main.tex @@ -575,13 +575,19 @@ However, when computing all tilt semistabilizers for $v$ on $\PP^2$, the maximum rank that appears turns out to be $\sage{extravagant.actual_rmax}$. \end{example} -\section{B.Schmidt's Method} +\section{B.Schmidt's Wall Finding Method} -Goals: -\begin{itemize} - \item intro - \item link repo -\end{itemize} +The proof for the previous theorem was hinted at in [ref], but the value appears +explicitly in [ref]. The latter reference is a SageMath [ref?] library for +computing certain quantities related to Bridgeland stabilities on Picard rank 1 +varieties. It also includes functions to compute pseudo-walls and +pseudo-semistabilizers for tilt stability. + +Here is an outline of the algorithm involved to do this. Simplifications will be +made in the presenteation to concentrate on the case we are interested in: +finding all pseudo-walls when $\beta_{-}\in\QQ$. In section [ref], a different +algorithm will be presented making use of the later theorems in this article, +with the goal of cutting down the run time. \subsection{Strategy} @@ -594,6 +600,38 @@ Goals: \item Stop when conditions fail \item method works same way for both rational beta_{-} but also for walls larger than certain amount + +Fix a Chern character $v$ with positive rank, $\Delta(v) \geq 0$, +and $\beta_{-}(v) \in \QQ$. +The goal is to find all Chern characters $u=(r,c\ell,d\ell^2)$ which satisfy the +conditions of lemma \ref{lem:pseudo_wall_numerical_tests} using +$P=(\beta_{-},0)$, as well as the Bogomolov inequalities: +$\Delta(u),\Delta(v-u) \geq 0$ and $\Delta(u)+\Delta(v-u) \leq \Delta(v)$. +We want to restrict our attention to pseudo-walls left of $V_v$ (condition (a) of +lemma), because this is the side of $V_v$ containing the chamber for Gieseker +stable objects, and the picture on the other side should be symmetric. +Condition (c) of the lemma is there to restrict to objects most likely to +semistabilizers of actual sheaves. The Chern characters which destabilize +`outwards' can be recovered as $v-u$ for each solution $u$ to the current +problem. + +To do this, first calculate the upper bound $r_{max}$ on the ranks of tilt +semistabilizers, as given by theorem \ref{thm:loose-bound-on-r}. + +Recalling consequence 2 of lemma \ref{lem:pseudo_wall_numerical_tests}, we can +iterate through the possible values of $\mu(u)=\frac{c}{r}$ taking a decreasing +sequence of all fractions between $\mu(v)$ and $\beta_{-}$, who's denominators +are no large than $r_{max}$ (giving a finite sequence). This can be done with Farey sequences [ref], for +which there exist formulae to generate. + +These $\mu(u)$ values determine pairs $r,c$ up to multiples, we can then take +all multiples which satisy $0<r\geq r_{max}$. + +We now have a finite sequence of pairs $r,c$ for which there might be a solution +to our problem. In particular, any $(r,c\ell,d\ell^2)$ satisfies consequence 2 +of lemma \ref{lem:pseudo_wall_numerical_tests}, and the positive rank condition. + + \end{itemize} \subsection{Limitations}