# All Questions

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### Physical interpretation of categorical structures related to Dirichlet Branes

In Dirichlet Branes and Mirror Symmetry by Aspinwall et al, section 5.9 discusses various questions that remain open. In particular they say: "There are many constructions from homological ...
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### Is there a name for connected graphs $G$ in which every vertex $v$ has a unique vertex $v'$ at distance $d$ where $d$ is the diameter of $G$?

Alternatively, what is known about such graphs? Examples are cycle graphs $C_{2n}$ as well as the Platonic graphs (except of course the tetrahedral graph $K_4$).
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### What is the probability of two random positive integers being both nonsquare? [closed]

Suppose we pick two integers m and n at randomly and independently from the set {1,2,3.......N}. What is the probability that both m and n are nonsquares?By a nonsquare I mean a positive integer ...
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### econometric transformation of variables

I would like to ask a question, which has been already asked, however I dind´t fully understand the answer and nobody replied to my edit question..maybe you can give me a arithmetic example for one ...
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### How should we think of maps to the intial object?

A final object in a category is one that has a unique map from any other object. An intuitive way of thinking about the final object is as the 'point'. Then we think of maps from the 'point' to ...
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### Find all integer solutions: $x^4+x^3+x^2+x=y^2$

Find all integer solutions of the following equation: $$x^4+x^3+x^2+x=y^2$$
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### How is the Standard Error and the Unbiased Estimate of the Variance Related?

I am going through a statistics textbook and there are two similar formula's that I cannot seem to grasp, one under the "Sampling Error" section and the other under the "Unbiased Estimator" section. ...
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### Semi-direct product of groups with one of them cyclic

Let $K$ be a cyclic group. Let $\phi,\psi: K\rightarrow Aut(H)$ be group homomorphisms such that there exists $\zeta\in Aut(H)$ satisfying $\phi(K)=\zeta \psi(K)\zeta^{-1}$. Then can we prove ...
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### How to write a maple program to calculate the sum of products of polynomial factors missing the factor in the sum?

How to write a maple program to find the sum of the products given below $\sum\limits_{i=1}^n a_i~\prod\limits_{j=1,j\neq i}^ns-b_j$
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### Find max: $\frac{a}{b+2a}+\frac{b}{c+2b}+\frac{c}{a+2c}$

For $a,b,c>0$ and $abc=1$. Find max: $\frac{a}{b+2a}+\frac{b}{c+2b}+\frac{c}{a+2c}$
### Find max: $M=\frac{a}{b^2+c^2+a}+\frac{b}{c^2+a^2+b}+\frac{c}{a^2+b^2+c}$
For $a,b,c>0$ and $abc=1$. Find max: $M=\frac{a}{b^2+c^2+a}+\frac{b}{c^2+a^2+b}+\frac{c}{a^2+b^2+c}$