Monday, 8 June 2015

linear algebra - ntimesn matrix with all eigenvalues equal to 1 or 0. Does a conjugated matrix with only 1's and 0's exist?



Let A be an n×n matrix with all eigenvalues equal to 1 or 0. Is there a conjugated matrix B=XAX1 for some X such that all the elements equal either 1 or 0?



My thoughts so far:

A is not necessarily positive semi-definite..



Given the assumption that A has only eigenvalues that are 0 or 1 doesn't really imply anything obvious that we can use. I don't see why there would be a conjugated matrix with all the elements equal either to 1 or 0.



So I'm currently trying to come up with a counterexample...



Edit: Actually, a counterexample might be the wrong path to take. The question is just asking for the existence of such a matrix...



Thanks in advance,


Answer




Hint: Jordan normal form. Note that since every field contains 1 and 0, the Jordan form of your A always exists, even if the underlying field is not algebraically closed.


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