Douglas S. Stones
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 Sep 2 answered Can This Matrix Proof Be Done Without the Definition? Sep 1 answered Graph Theory / Networks … Triadic Closure and Strong/Weak Ties Aug 31 comment In how many ways can three numbers be selected from the numbers $1,2,\dots,300$ such that their sum is divisible by $3$? Aside from the above, I found yours the best answer. Right to the point! Aug 31 comment In how many ways can three numbers be selected from the numbers $1,2,\dots,300$ such that their sum is divisible by $3$? I'd say the answer to that question is yes (but I don't know what it is). Aug 31 answered In how many ways can three numbers be selected from the numbers $1,2,\dots,300$ such that their sum is divisible by $3$? Aug 31 comment In how many ways can three numbers be selected from the numbers $1,2,\dots,300$ such that their sum is divisible by $3$? In the $(0,1,2)$ case, we can choose $100^3$ triples. Aug 31 revised Factorising complex equations edited tags Aug 31 reviewed Reviewed Want to clarify whether I am correct or not, $\Phi(G) \subseteq \Phi(H)$? Aug 30 revised A problem on limit added 137 characters in body Aug 30 comment For what $n$ can $\pm 1\pm 2\pm 3 … \pm (n-1) \pm n = n+1$? That's an assertion. Could you add a proof of this assertion into this answer? Aug 30 comment Find order of $xy$ provided $x^2=e, y^3=e$ and $yxy=xy^2x$ It's somewhat implicit that saying e.g. "$x^2=e$" implies $x$ has order $2$, otherwise we'd instead say "$x=e$" (or not even introduce $x$). Perhaps I'm a bit too pedantic (but this kind of detail matters e.g. for automated theorem proving). Anyway, the answer is fine so I better +1 it. Aug 30 comment Find order of $xy$ provided $x^2=e, y^3=e$ and $yxy=xy^2x$ Hmm... it could be that $x=e=y$ too (in which case $xy=e$ has order $1$). The question doesn't say e.g. "the order of $x$ is $2$". [It must be a divisor of 3, though. So it's either $3$ or $1$.] Aug 30 revised Find order of $xy$ provided $x^2=e, y^3=e$ and $yxy=xy^2x$ added 8 characters in body; edited tags; edited title Aug 29 revised How is $\{ (1/n , 1 + 1/n) \}_{n \geq 1}$ a cover for $(0,2)$? edited title Aug 29 comment Problem on directed graph involving $\gcd$ The question for strongly connected digraphs is now here. Aug 29 comment Problem on directed graph involving $\gcd$ It looks like a counterexample to me. I wonder if this is a homework question; the lecturer might have a surprise when the assignments are returned. (I suppose the theorem would be true if there were no "incoherent" cycles.) Aug 29 revised Problem on directed graph involving $\gcd$ Added drawing of graph Aug 29 comment Problem on directed graph involving $\gcd$ What is the value of $p$ if $G$ has no cycles? Aug 29 comment Calculate the Determinant? I neatened this answer up a bit, and also corrected the arithmetic. Aug 29 revised Calculate the Determinant? Neatened it up; corrected arithmetic.