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Commit 99dbc164 authored by Luke Naylor's avatar Luke Naylor
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Complete explanation for Schmidt's algorithm

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......@@ -589,7 +589,7 @@ 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}
\subsection*{Problem statement}
Goals:
\begin{itemize}
......@@ -600,6 +600,7 @@ Goals:
\item Stop when conditions fail
\item method works same way for both rational beta_{-} but also for walls
larger than certain amount
\end{itemize}
Fix a Chern character $v$ with positive rank, $\Delta(v) \geq 0$,
and $\beta_{-}(v) \in \QQ$.
......@@ -615,6 +616,9 @@ semistabilizers of actual sheaves. The Chern characters which destabilize
`outwards' can be recovered as $v-u$ for each solution $u$ to the current
problem.
\subsection*{Algorithm}
\subsubsection*{Finding possible $r$ and $c$}
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}.
......@@ -625,16 +629,27 @@ are no large than $r_{max}$ (giving a finite sequence). This can be done with Fa
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 $0<r\geq r_{max}$.
all multiples which satisy $0<r\leq r_{max}$.
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.
$(r,c\ell,d\ell^2)$ 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. What remains is to find the $d$ values which satisfy
the Bogomolov inequalities and consequence 3 of lemma
\ref{lem:pseudo_wall_numerical_tests}
($\chern_2^{\beta_{-}}(u)>0$).
\subsubsection*{Finding $d$ for fixed $r$ and $c$}
$\Delta(u) \geq 0$ induces an upper bound $\frac{c^2}{2r}$ on $d$, and the
$\chern_2^{\beta_{-}}(u)>0$ condition induces a lower bound on $d$.
The values in the range can be tested individually, to check that
the rest of the conditions are satisfied.
\end{itemize}
\subsection{Limitations}
\subsection*{Limitations}
Goals:
\begin{itemize}
......
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