## Maximal length vector under constraints

Consider a criculant symmetric $M$ an $n \times n$ matrix with $0$ and $1$ entries and $r$ entries of $1$ in each row with the diagonal values taken as $1$. I am looking for a $0-1$ vector $v$ with the largest hamming weight such that $\langle v , \frac{1}{r}Mv \rangle$ $=$ $\langle v , v \rangle$.

I am also looking for the rate of growth in the hamming weight as $m \rightarrow \infty$, $\langle v , \frac{1}{r^{m}}M^{\otimes{m}}v \rangle$ $=$ $\langle v , v \rangle$. What are some good mathematical techniques/tools to study this kind of problems?

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Perhaps I misunderstand, but if $v$ is all ones (and you can't get a bigger Hamming weight than that) then $Mv$ is all $r$, so $(1/r)Mv$ is all ones again, so $(1/r)Mv=v$ and the inner product of $v$ with $(1/r)Mv$ is the inner product of $v$ with $v$.

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 I think I am thinking something else. may be I need to rephrase a bit! – unknown (yahoo) Nov 20 2011 at 0:12 I will probably post another post! Thankyou! – unknown (yahoo) Nov 20 2011 at 0:14