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luke naylor latex documents
research
Max Destabilizer Rank
Commits
99dbc164
Commit
99dbc164
authored
1 year ago
by
Luke Naylor
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Complete explanation for Schmidt's algorithm
parent
dd43105a
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99dbc164
...
...
@@ -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
\
g
eq
r
_{
max
}$
.
all multiples which satisy
$
0
<r
\
l
eq
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
}{
2
r
}$
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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