Modular invariant theory: Difference between revisions

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:<math>\begin{vmatrix} x_1 & x_1^q & x_1^{q^2}\\x_2 & x_2^q & x_2^{q^2}\\x_3 & x_3^q & x_3^{q^2} \end{vmatrix}</math>
 
Then under the action of an element ''g'' of GL<sub>''n''</sub>('''F'''<sub>''q''</sub>) these determinants are all multiplied by det(''g''), so they are all invariants of SL<sub>''n''</sub>('''F'''<sub>''pq''</sub>) and the ratios [''e''<sub>1</sub>, ...,''e''<sub>''n''</sub>]/[0,&nbsp;1,&nbsp;...,''n''&nbsp;&minus;&nbsp;1] are invariants of GL<sub>''n''</sub>('''F'''<sub>''q''</sub>), called '''Dickson invariants'''. Dickson proved that the full ring of invariants '''F'''<sub>''q''</sub>[''X''<sub>1</sub>, ...,''X''<sub>''n''</sub>]<sup>GL<sub>''n''</sub>('''F'''<sub>''q''</sub>)</sup> is a polynomial algebra over the ''n'' Dickson invariants [0,&nbsp;1,&nbsp;...,''i''&nbsp;&minus;&nbsp;1,&nbsp;''i''&nbsp;+&nbsp;1,&nbsp;...,&nbsp;''n'']/[0,1,...,''n''&minus;1] for ''i''&nbsp;=&nbsp;0, 1, ..., ''n''&nbsp;&minus;&nbsp;1.
{{harvtxt|Steinberg|1987}} gave a shorter proof of Dickson's theorem.