diff --git a/tex/bounds-on-semistabilisers.tex b/tex/bounds-on-semistabilisers.tex index b6b9aa1b52cbdf7e352356c5d5e73cbfb5589e27..805089b2d7789d09c214cff0acf85da6fed432d6 100644 --- a/tex/bounds-on-semistabilisers.tex +++ b/tex/bounds-on-semistabilisers.tex @@ -131,18 +131,21 @@ rank that appears turns out to be $\sage{extravagant.actual_rmax}$. \section{Tighter Bounds} \label{sec:refinement} -To get tighter bounds on the rank of destabilisers $E$ of some $F$ with some -fixed Chern character, we will need to consider each of the values which -$\chern_1^{\beta}(E)$ can take. -Doing this will allow us to eliminate possible values of $\chern_0(E)$ for which -each $\chern_1^{\beta}(E)$ leads to the failure of at least one of the inequalities. -As opposed to only eliminating possible values of $\chern_0(E)$ for which all -corresponding $\chern_1^{\beta}(E)$ fail one of the inequalities (which is what +To get tighter bounds on the rank of solutions $u$ to the Problems +\ref{problem:problem-statement-1} and +\ref{problem:problem-statement-2}, +we will need to consider each of the values which +$\chern_1^{\beta}(u)$ can take. +Doing this will allow us to eliminate possible values of $\chern_0(u)$ for which +each $\chern_1^{\beta}(u)$ leads to the failure of at least one of the inequalities. +As opposed to only eliminating possible values of $\chern_0(u)$ for which all +corresponding $\chern_1^{\beta}(u)$ fail one of the inequalities (which is what was implicitly happening before). -First, let us fix a Chern character for $F$, and some pseudo-semistabiliser -$u$ which is a solution to problem +First, let us fix a Chern character $v$ with $\Delta(v)\geq 0$, +$\chern_0(v)>0$, or $\chern_0(v)=0$ and $\chern_1(v)>0$, +and some solution $u$ to the Problem \ref{problem:problem-statement-1} or \ref{problem:problem-statement-2}. Take $\beta = \beta(P)$ where $P\in\Theta_v^-$ is the choice made in problem @@ -155,8 +158,8 @@ Take $\beta = \beta(P)$ where $P\in\Theta_v^-$ is the choice made in problem \\ u \coloneqq& \:(r,c\ell,d\ell^2) && \text{where $r,c\in \ZZ$ and $d\in \frac{1}{\lcm(m,2)}\ZZ$} + \label{eqn:u-coords} \end{align} - Recall from condition \ref{item:chern1bound:lem:num_test_prob1} in @@ -177,7 +180,7 @@ from plots_and_expressions import c_in_terms_of_q \qquad 0 \leq q \coloneqq \chern_1^{\beta}(u) \leq \chern_1^{\beta}(v) \end{equation} -Furthermore, $\chern_1 \in \ZZ$ so we only need to consider +Furthermore, if $\beta$ is rational, $\chern_1 \in \ZZ$ so we only need to consider $q \in \frac{1}{n} \ZZ \cap [0, \chern_1^{\beta}(F)]$, where $n$ is the denominator of $\beta$. For the next subsections, we consider $q$ to be fixed with one of these values, @@ -189,6 +192,8 @@ and we shall be varying $\chern_0(E) = r$ to see when certain inequalities fail. This section studies the numerical conditions that $u$ must satisfy as per lemma \ref{lem:num_test_prob1} (or corollary \ref{cor:num_test_prob2}) +and reformulates them as bounds on $d$ from Equation \ref{eqn:u-coords}. +This is done to determine which $r$ values lead to no possible values for $d$. \subsubsection{Size of pseudo-wall\texorpdfstring{: $\chern_2^P(u)>0$}{}} \label{subsect-d-bound-radiuscond} @@ -197,7 +202,6 @@ This condition refers to condition \ref{item:radiuscond:lem:num_test_prob1} from Lemma \ref{lem:num_test_prob1} (or corollary \ref{cor:num_test_prob2}). - In the case where we are tackling problem \ref{problem:problem-statement-2} (with $\beta = \beta_{-}$), this condition, when expressed as a bound on $d$, amounts to: @@ -434,14 +438,13 @@ for the bounds on $d$ in terms of $r$ is illustrated in Figure The question of whether there are pseudo-destabilisers of arbitrarily large rank, in the context of the graph, comes down to whether there are points $(r,d) \in \ZZ \oplus \frac{1}{\lcm(m,2)} \ZZ$ (with large $r$) -% TODO have a proper definition for pseudo-destabilizers/walls that fit above the yellow line (ensuring positive radius of wall) but below the blue and green (ensuring $\Delta(u), \Delta(v-u) > 0$). These lines have the same assymptote at $r \to \infty$ (eqns \ref{eqn:bgmlv2_d_bound_betamin}, \ref{eqn:bgmlv3_d_bound_betamin}, \ref{eqn:radiuscond_d_bound_betamin}). -As mentioned in the introduction (sec \ref{sec:intro}), the finiteness of these +As mentioned in the introduction to this Part, the finiteness of these solutions is entirely determined by whether $\beta$ is rational or irrational. Some of the details around the associated numerics are explored next. @@ -542,7 +545,7 @@ the lower bound on $d$ is equal to one of the upper bounds on $d$ (i.e. finding certain intersection points of the graph in Figure \ref{fig:problem1:d_bounds_xmpl_gnrc_q}). -\begin{lemma}[Problem \ref{problem:problem-statement-1} upper Bound on $r$] +\begin{theorem}[Problem \ref{problem:problem-statement-1} upper Bound on $r$] \label{lem:prob1:r_bound} Let $u$ be a solution to problem \ref{problem:problem-statement-1} and $q\coloneqq\chern_1^{B}(u)$. @@ -550,7 +553,7 @@ the lower bound on $d$ is equal to one of the upper bounds on $d$ \begin{equation} \sage{problem1.r_bound_expression} \end{equation} -\end{lemma} +\end{theorem} \begin{proof} Recall that $d\coloneqq\chern_2(u)$ has two upper bounds in terms of $r$: in @@ -578,14 +581,14 @@ But given that $0 \leq q \leq \chern_1^{B}(v)$, we can take the maximum of this bound, over $q$ in this range, to get a simpler (but weaker) bound in the following Lemma \ref{lem:prob1:convenient_r_bound}. -\begin{lemma} +\begin{theorem}[Problem \ref{problem:problem-statement-1} global upper Bound on $r$] \label{lem:prob1:convenient_r_bound} Let $u$ be a solution to problem \ref{problem:problem-statement-1}. Then $r\coloneqq\chern_0(u)$ is bounded above by the following expression: \begin{equation} \sage{problem1.r_max} \end{equation} -\end{lemma} +\end{theorem} \begin{proof} The first term of the minimum in Lemma \ref{lem:prob1:r_bound} @@ -599,11 +602,11 @@ following Lemma \ref{lem:prob1:convenient_r_bound}. \end{proof} -\begin{note} +\begin{remark} $q_{\mathrm{max}} > 0$ is immediate from the expression, but $q_{\mathrm{max}} \leq \chern_1^{B}(v)$ is equivalent to $\Delta(v) \geq 0$, which is true by assumption in this setting. -\end{note} +\end{remark} \subsection{Bounds on Semistabilizer Rank \texorpdfstring{$r$}{} in Problem @@ -614,7 +617,7 @@ Now, the inequalities from the above subsubsection each given $q=\chern^{\beta}_1(E)$, how large $r$ needs to be in order to leave no possible solutions for $d$. At that point, there are no solutions $u=(r,c\ell,d\ell^2)$ to problem \ref{problem:problem-statement-2}. -The strategy here is similar to what was shown in theorem +The strategy here is similar to what was shown in Theorem \ref{thm:loose-bound-on-r}. @@ -747,7 +750,7 @@ from plots_and_expressions import q_sol, bgmlv_v, psi \begin{proof} The ranks of the pseudo-semistabilisers for $v$ are bounded above by the -maximum over $q\in [0, \chern_1^{\beta}(F)]$ of the expression in theorem +maximum over $q\in [0, \chern_1^{\beta}(F)]$ of the expression in Theorem \ref{thm:rmax_with_uniform_eps}. Noticing that the expression is a maximum of two quadratic functions in $q$: \begin{equation*} @@ -813,7 +816,7 @@ this value of $\frac{1}{2n^2}\ZZ$ explicitly. The expressions that will follow will be a bit more complicated and have more parts which depend on the values of $q$ and $\beta$, even their numerators -$\aa,\bb$ specifically. The upcoming Theorem (TODO ref) is less useful as a +$\aa,\bb$ specifically. The upcoming Theorem \ref{thm:rmax_with_eps1} is less useful as a `clean' formula for a bound on the ranks of the pseudo-semistabilisers, but has a purpose in the context of writing a computer program to find pseudo-semistabilisers. Such a program would iterate through possible values of