Plücker coordinates: Difference between revisions

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Rational points: Clarify some point about torsion
Sintel (talk | contribs)
Height: Clarify lattice volume, add wikipedia links
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We can define the height of a rational point simply as the Euclidean norm on its Plücker coordinates <math>X = \iota (P)</math>.
We can define the height of a rational point simply as the Euclidean norm on its Plücker coordinates <math>X = \iota (P)</math>.
:<math>
:<math>
H(P) = \left\| X \right\| = \left\| p_1 \wedge \ldots \wedge p_n \right\| \\
H(P) = \left\| X \right\| = \left\| m_1 \wedge \ldots \wedge m_n \right\| \\
</math>
</math>


This is equivalent to the covolume of the lattice defined by P (also know as the lattice determinant), which can be easily computed using the Gram matrix.
In terms of the lattice defined by P, this definition is equivalent to the volume of the {{w|fundamental domain}}, also known as the lattice determinant.
It is easy to show that this does not depend on the basis we choose.
 
The height can be easily computed using the {{w|Gram matrix}}:
:<math>
:<math>
\begin{align}
\begin{align}
\mathrm{G}_{ij} &= \left\langle p_i, p_j \right\rangle \\
\mathrm{G}_{ij} &= \left\langle m_i, m_j \right\rangle \\
\sqrt{\det(\mathrm{G})} &= \left\| p_1 \wedge \ldots \wedge p_n \right\| = \left\| X \right\| \, .
\sqrt{\det(\mathrm{G})} &= \left\| m_1 \wedge \ldots \wedge m_n \right\| = \left\| X \right\| \, .
\end{align}
\end{align}
</math>
</math>