- Commit
- bec199c9350b1e8f5e1ad6d5f56516577a6e73a6
- Parent
- c3789a205e7abf6f081baa150631150dcf3d559a
- Author
- Pablo <pablo-escobar@riseup.net>
- Date
Changed the notation in an example
Source code for my notes on representations of semisimple Lie algebras and Olivier Mathieu's classification of simple weight modules
Changed the notation in an example
1 file changed, 7 insertions, 7 deletions
Status | File Name | N° Changes | Insertions | Deletions |
Modified | sections/complete-reducibility.tex | 14 | 7 | 7 |
diff --git a/sections/complete-reducibility.tex b/sections/complete-reducibility.tex @@ -80,15 +80,15 @@ this is not always the case. For instance\dots \begin{example}\label{ex:indecomposable-not-irr} The space \(V = K^2\) endowed with the homomorphism of Lie algebras \begin{align*} - \rho : K[x] & \to \mathfrak{gl}(V) \\ - x & \mapsto \begin{pmatrix} 1 & 1 \\ 0 & 1 \end{pmatrix} + x \cdot e_1 & = e_1 & x \cdot e_2 = e_1 + e_2 \end{align*} is a representation of the Lie algebra \(K[x]\). Notice \(V\) has a single - nonzero proper subrepresentation, which is spanned by the vector \((1, 0)\). - This is because if \((a + b, b) = \rho(x) \ (a, b) = \lambda (a, b)\) for - some \(\lambda \in K\) then \(\lambda = 1\) and \(b = 0\). Hence \(V\) is - indecomposable -- it cannot be broken into a direct sum of \(1\)-dimensional - subrepresentations -- but it is evidently not irreducible. + nonzero proper subrepresentation, which is spanned by the vector \(e_1\). + This is because if \((a + b) e_1 + b e_2 = x \cdot (a e_1 + b e_2) = \lambda + \cdot (a e_1 + b e_2)\) for some \(\lambda \in K\) then \(\lambda = 1\) and + \(b = 0\). Hence \(V\) is indecomposable -- it cannot be broken into a direct + sum of \(1\)-dimensional subrepresentations -- but it is evidently not + irreducible. \end{example} This counterexample poses an interesting question: are there conditions one can