- #1
gerben
- 511
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I read the following on the wikipedia page about simple rings (http://en.wikipedia.org/wiki/Simple_ring):
I do not see why this is the case. Take the ring of 3 by 3 matrices over the real numbers and the left ideal, J, generated by:
[tex]
\begin{pmatrix}
0 &1 &1\\
0 &0 &0\\
0 &0 &0
\end{pmatrix}
[/tex]
then J is not equal to S = {M ∈ M(3,ℝ) | The 1st column of M has zero entries},
since for example the following matrix is in S but not in J:
[tex]
\begin{pmatrix}
0 &1 &0\\
0 &0 &1\\
0 &0 &0
\end{pmatrix}
[/tex]
Can anybody help me understand what the wikipedia page is trying to say, or where I am seeing things wrong?
Let D be a division ring and M(n,D) be the ring of matrices with entries in D. It is not hard to show that every left ideal in M(n,D) takes the following form:
{M ∈ M(n,D) | The n1...nk-th columns of M have zero entries},
for some fixed {n1,...,nk} ⊂ {1, ..., n}.
I do not see why this is the case. Take the ring of 3 by 3 matrices over the real numbers and the left ideal, J, generated by:
[tex]
\begin{pmatrix}
0 &1 &1\\
0 &0 &0\\
0 &0 &0
\end{pmatrix}
[/tex]
then J is not equal to S = {M ∈ M(3,ℝ) | The 1st column of M has zero entries},
since for example the following matrix is in S but not in J:
[tex]
\begin{pmatrix}
0 &1 &0\\
0 &0 &1\\
0 &0 &0
\end{pmatrix}
[/tex]
Can anybody help me understand what the wikipedia page is trying to say, or where I am seeing things wrong?
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