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Commit 3e2de5e9 authored by Luke Naylor's avatar Luke Naylor
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Outline the new algorithm

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......@@ -745,6 +745,7 @@ problem with the help of lemma \ref{lem:pseudo_wall_numerical_tests}.
\item $\Delta(v-u) \geq 0$
\label{item:bgmlvv-u:lem:num_test_prob2}
\item $\mu(u)=\frac{c}{r}<\mu(v)$
\label{item:mubound:lem:num_test_prob2}
\item $0\leq\chern_1^{\beta_{-}}(u)\leq\chern_1^{\beta_{-}}(v)$
\label{item:chern1bound:lem:num_test_prob2}
\item $\chern_2^{\beta_{-}}(u)>0$
......@@ -2105,6 +2106,93 @@ Goals:
\item Relate to numerical condition described by Yanagida/Yoshioka
\end{itemize}
\section{Computing solutions to Problem \ref{problem:problem-statement-2}}
\label{sect:prob2-algorithm}
Alongside this article, there is a library \cite{NaylorRust2023} to compute
the solutions to problem \ref{problem:problem-statement-2}, using the theorems
above.
The way it works, is by yielding solutions to the problem
$u=(r,c\ell,\frac{e}{2}\ell^2)$ as follows.
\subsection{Iterating Over Possible $q=\chern^{\beta_{-}}(u)$}
Given a Chern character $v$, the domain of the problem are first verified: that
$v$ has positive rank, that it satisfies $\Delta(v) \geq 0$, and that
$\beta_{-}(v)$ is rational.
Take $\beta_{-}(v)=\frac{a_v}{n}$ in simplest terms.
Iterate over $q \in [0,\chern_1^{\beta_{-}}(v)]\cap\frac{1}{n}\ZZ$.
For any $u = (r,c\ell,\frac{e}{2}\ell^2)$, satisfying
$\chern_1^{\beta_{-}}(u)=q$ for one of the $q$ considered is equivalent to
satisfying condition \ref{item:chern1bound:lem:num_test_prob2}
in corollary \ref{cor:num_test_prob2}.
\subsection{Iterating Over Possible $r=\chern_0(u)$ for Fixed $q=\chern^{\beta_{-}}(u)$}
Let $q=\frac{b_q}{n}$ be one of the values of $\chern_1^{\beta_{-}}(u)$ that we
have fixed. As mentioned before, the only values of $r$ which can
give $\chern_1^{\beta_{-}}(u)=q$ are precisely the ones which satisfy
$a_v r \equiv b_q \pmod{n}$.
This is true for all integers when $\beta_{-}=0$ (and so $n=1$), but otherwise,
this is equivalent to
$r \equiv {a_v}^{-1}b_q \pmod{n}$, since $a_v$ and $n$ are coprime.
Note that expressing $\mu(u)$ in term of $q$ and $r$ gives:
\begin{align*}
\mu(u) & = \frac{c}{r} = \frac{q+r\beta_{-}}{r}
\\
&= \beta_{-} + \frac{q}{r}
\end{align*}
So condition \ref{item:mubound:lem:num_test_prob2} in corollary
\ref{cor:num_test_prob2} is satisfied at this point precisely when:
\begin{equation*}
r > \frac{q}{\mu(u) - \beta_{-}}
\end{equation*}
Note that the right hand-side is greater than, or equal, to 0, so such $r$ also
satisfies \ref{item:rankpos:lem:num_test_prob2}.
Then theorem \ref{thm:rmax_with_eps1} gives an upper on possible $r$ values
for which it is possible to satisfy conditions
\ref{item:bgmlvu:lem:num_test_prob2},
\ref{item:bgmlvv-u:lem:num_test_prob2}, and
\ref{item:radiuscond:lem:num_test_prob2}.
Iterate over such $r$ so that we are guarenteed to satisfy conditions
\ref{item:mubound:lem:num_test_prob2}, and
\ref{item:radiuscond:lem:num_test_prob2}
in corollary
\ref{cor:num_test_prob2}, and have a chance at satisfying the rest.
\subsection{Iterating Over Possible $d=\chern_2(u)$ for Fixed $r=\chern_0(u)$
and $q=\chern^{\beta_{-}}(u)$}
At this point we have fixed $\chern_0(u)=r$ and
$\chern_1(u)=c=q+r\beta_{-}$.
And the cases considered are precisely the ones which satisfy conditions
\ref{item:chern1bound:lem:num_test_prob2},
\ref{item:mubound:lem:num_test_prob2}, and
\ref{item:radiuscond:lem:num_test_prob2}
in corollary \ref{cor:num_test_prob2}.
It remains to find $\chern_2(u)=d=\frac{e}{2}$
which satisfy the remaining conditions
\ref{item:bgmlvu:lem:num_test_prob2},
\ref{item:bgmlvv-u:lem:num_test_prob2}, and
\ref{item:radiuscond:lem:num_test_prob2}.
These conditions induce upper and lower bounds on $d$, and it then remains to
just pick the integers $e$ that give $d$ values within the bounds.
Thus, through this process yielding all solutions $u=(r,c\ell,\frac{e}{2}\ell^2)$
to the problem for this choice of $v$.
\newpage
\printbibliography
......
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