Study HN: Linear Algebra 1, fortnight 2

Re:Study HN: Linear Algebra 1, fortnight 2 by impendia on Wednesday October 19, 2011 @07:59AM (#3129706)

I feel like there is unlikely to be a solution which doesn't involve (1) brute force, or (2) higher-level theory (i.e. eigenvectors and eigenvalues).

Prove me wrong, and I will be tripping over myself to upvote you ;)

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Re:Study HN: Linear Algebra 1, fortnight 2 by gruseom on Wednesday October 19, 2011 @12:21PM (#3130811)

Certainly it's artificial to restrict oneself to primitive concepts, unless of course you don't know about eigenvalues yet or forgot it all. :) And it is an exercise from the earliest chapter, so we're supposed to stay in simple-land.

Did you look at my solution (http://news.ycombinator.com/item?id=3129023)? There's no higher-level theory in it. Is it brute force? Not sure. At least it doesn't require solving any element-wise equations.

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Re:Study HN: Linear Algebra 1, fortnight 2 by impendia on Wednesday October 19, 2011 @02:03PM (#3131285)

It's elegant, but as far as I can see, your argument only holds for the single matrix C which you describe.

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Re:Study HN: Linear Algebra 1, fortnight 2 by gruseom on Wednesday October 19, 2011 @02:07PM (#3131306)

Oh, absolutely. The exercise is to construct one example.

If you were talking about solving the general case (For any C, find D such that CD = -DC) I can see why you wanted more powerful tools.

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Re:Study HN: Linear Algebra 1, fortnight 2 by impendia on Wednesday October 19, 2011 @03:26PM (#3131641)

oh! that's easier :)

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