\begin{equation} \DeclareMathOperator\Gr{Gr} \DeclareMathOperator\LGr{LGr} \DeclareMathOperator\OGr{OGr} \DeclareMathOperator\SGr{SGr} \DeclareMathOperator\Kzero{K_0} \DeclareMathOperator\index{i} \DeclareMathOperator\rk{rk} \end{equation}

Grassmannian.info

A periodic table of (generalised) Grassmannians.

Symplectic Grassmannian $\SGr(4,12)$

Y Z Y Z Y Z Y Z Y Z Y Z
Betti numbers
\begin{align*} \mathrm{b}_{ 0 } &= 1 \\ \mathrm{b}_{ 2 } &= 1 \\ \mathrm{b}_{ 4 } &= 2 \\ \mathrm{b}_{ 6 } &= 3 \\ \mathrm{b}_{ 8 } &= 5 \\ \mathrm{b}_{ 10 } &= 6 \\ \mathrm{b}_{ 12 } &= 8 \\ \mathrm{b}_{ 14 } &= 10 \\ \mathrm{b}_{ 16 } &= 12 \\ \mathrm{b}_{ 18 } &= 14 \\ \mathrm{b}_{ 20 } &= 15 \\ \mathrm{b}_{ 22 } &= 17 \\ \mathrm{b}_{ 24 } &= 17 \\ \mathrm{b}_{ 26 } &= 18 \\ \mathrm{b}_{ 28 } &= 17 \\ \mathrm{b}_{ 30 } &= 17 \\ \mathrm{b}_{ 32 } &= 15 \\ \mathrm{b}_{ 34 } &= 14 \\ \mathrm{b}_{ 36 } &= 12 \\ \mathrm{b}_{ 38 } &= 10 \\ \mathrm{b}_{ 40 } &= 8 \\ \mathrm{b}_{ 42 } &= 6 \\ \mathrm{b}_{ 44 } &= 5 \\ \mathrm{b}_{ 46 } &= 3 \\ \mathrm{b}_{ 48 } &= 2 \\ \mathrm{b}_{ 50 } &= 1 \\ \mathrm{b}_{ 52 } &= 1 \end{align*}
Basic information
dimension
26
index
9
Euler characteristic
240
Betti numbers
$\mathrm{b}_{ 0 } = 1$, $\mathrm{b}_{ 2 } = 1$, $\mathrm{b}_{ 4 } = 2$, $\mathrm{b}_{ 6 } = 3$, $\mathrm{b}_{ 8 } = 5$, $\mathrm{b}_{ 10 } = 6$, $\mathrm{b}_{ 12 } = 8$, $\mathrm{b}_{ 14 } = 10$, $\mathrm{b}_{ 16 } = 12$, $\mathrm{b}_{ 18 } = 14$, $\mathrm{b}_{ 20 } = 15$, $\mathrm{b}_{ 22 } = 17$, $\mathrm{b}_{ 24 } = 17$, $\mathrm{b}_{ 26 } = 18$, $\mathrm{b}_{ 28 } = 17$, $\mathrm{b}_{ 30 } = 17$, $\mathrm{b}_{ 32 } = 15$, $\mathrm{b}_{ 34 } = 14$, $\mathrm{b}_{ 36 } = 12$, $\mathrm{b}_{ 38 } = 10$, $\mathrm{b}_{ 40 } = 8$, $\mathrm{b}_{ 42 } = 6$, $\mathrm{b}_{ 44 } = 5$, $\mathrm{b}_{ 46 } = 3$, $\mathrm{b}_{ 48 } = 2$, $\mathrm{b}_{ 50 } = 1$, $\mathrm{b}_{ 52 } = 1$
$\mathrm{Aut}^0(\SGr(4,12))$
$\mathrm{PSp}_{ 12 }$
$\pi_0\mathrm{Aut}(\SGr(4,12))$
$1$
$\dim\mathrm{Aut}^0(\SGr(4,12))$
78
Projective geometry
minimal embedding

$\SGr(4,12)\hookrightarrow\mathbb{P}^{ 428 }$

degree
35354908160
Hilbert series
1, 429, 49686, 2598960, 78279696, 1563867162, 22706917233, 255239407995, 2324943942750, 17759263501980, 116800354642608, 675304542362112, 3490123185010176, 16344821411246160, 70146592552402236, 278490191930132754, 1030973785534844151, 3583187691063762705, 11760159071184345250, 36633424289800338000, ...
Projective duality

The projective dual is a hypersurface.

codimension
1
degree
109701288
self-dual
no

[Tevelev, Theorems 9.19 and 10.22 (arXiv version)] [Tevelev, Theorems 7.1–7.2 (arXiv version)] All Grassmannians.

Exceptional collections

Full exceptional collections in $\mathbf D^{\mathrm b}(\SGr(4,12))$:

Quantum cohomology
small
not generically semisimple [Galkin–Leung–Li–Xiong, Theorem 1.2]

Graded dimensions modulo the index $9$: $\widetilde b_{ 2 }=27>26=\widetilde b_{ 1 }$, where $1\equiv 5\cdot 2\pmod{ 9 }$.

big
generically semisimple [Li–Liu–Yu–Zhang, Theorems 1.2 and 1.4]

Convergent near the large-radius limit.

Eigenvalues of quantum multiplication by $\mathrm{c}_1(\SGr(4,12))$:

Homological projective duality

No Lefschetz decomposition recorded. Fullness of the Kuznetsov–Polishchuk collection does not give a Lefschetz decomposition. [Kuznetsov–Polishchuk] [Guseva–Novikov, Theorem 1.2]

No HP-dual model recorded.

$k$-Fanoness

Fano but not 2-Fano. [Araujo et al., Theorems 1.3 and 1.4]

References
  1. Kuznetsov, Alexander; Polishchuk, Alexander. Exceptional collections on isotropic Grassmannians. J. Eur. Math. Soc. (JEMS) 18 (2016), 507–574. MR3463417.
  2. Carolina Araujo; Roya Beheshti; Ana-Maria Castravet; Kelly Jabbusch; Svetlana Makarova; Enrica Mazzon; Libby Taylor; Nivedita Viswanathan. Higher Fano Manifolds. Rev. Un. Mat. Argentina 64 (2022), 103–125. arXiv:2110.02339.
  3. Alexander Samokhin; Wilberd van der Kallen. Highest weight category structures on $\operatorname{rep}(B)$ and full exceptional collections on generalized flag varieties over $\mathbb Z$. Preprint (2024). arXiv:2407.13653.
  4. Sergey Galkin; Naichung Conan Leung; Changzheng Li; Rui Xiong; appendix by Pieter Belmans and Markus Reineke. A-D-E diagrams, Hodge–Tate hyperplane sections and semisimple quantum cohomology. Preprint (2025). arXiv:2509.01101.
  5. Lyalya Guseva; Alexander Novikov. Full exceptional collections on the symplectic isotropic Grassmannians. Advances in Mathematics (2026), article 111211. arXiv:2505.13005.
  6. Changzheng Li; Zhaoyang Liu; Tony Yue Yu; Chi Zhang. Convergence and semisimplicity of big quantum cohomology of flag varieties. Preprint (2026). arXiv:2610.28418.

All references.