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0 votes
1 answer
4 views
Showing positive definite quadratic forms give the "most symmetrical" metrics over $\mathbb{R}^n$
I was unsatisfied with the many proofs of the Pythagorean theorem in which it's not clearly apparent which axioms are specifically needed, or because said axioms seem too geometrically motivated in ...
0 votes
0 answers
4 views
On the dimension of linear system to give embedding in $\mathbb{P}^3$
On p. 353 of Algebraic Geometry, Hartshorne poses the question of whether a curve of degree $7$ with $g=5$ exists in $\mathbb{P}^3$. He then says ``We need a very ample divisor $D$ of degree $7$, with ...
1 vote
0 answers
12 views
Characterization of the $\sigma$-ideal generated by wandering sets for a measureable system $(X,\mathcal{B},T)$
Let $(X, \mathcal{B}, T)$ be a measureable dynamical system, meaning that $T : X \rightarrow X$ is a Borel automorphism over a standard Borel space $(X, \mathcal{B})$. A measureable set $W$ is called ...
0 votes
1 answer
55 views
I'm struggling with a logic problem and need some help understanding my mistake
The Problem A duck has two legs. When a duck folds one leg, only one leg is visible. When a duck is sitting, neither of its legs is visible. When Roman went to the lake, there were 33 ducks. He ...
-1 votes
0 answers
15 views
CW-structure on $ X = S^1\times\partial D^2 \;\cup\; \{x,y\}\times D^2 \subset T=S^1\times D^2. $
Considering the space, $ X = S^{1} \times \partial D^{2} \,\cup\, \{x, y\} \times D^{2}. $ the subspace of the solid torus $ S^{1} \times D^{2} $ given by the union of the boundary of the boundary ...
0 votes
1 answer
21 views
Equivalences of a generator module
I came across Kasch's definition of a module that is a generator in a category of modules, namely, that a module $C$ is a generator if for every $M$ in that category of modules $$ 0 = \operatorname{...
2 votes
0 answers
41 views
For which $n$ and $k$ does there exist a "cursed" centrifuge arrangement?
For background, say that a centrifuge has $n$ slots arranged in a circle and $k$ tubes are placed within it. This is equivalent to choosing $k$ distinct $n$-th roots of unity. The centrifuge is ...
3 votes
1 answer
56 views
Dirac Delta question: does $\int_{-\infty}^{\infty}f(t)\,\delta(t-\tau)\,\mathrm dt=\int_{-\infty}^{\infty}f(t)\,\delta(\tau-t)\,\mathrm dt$? [duplicate]
For a recent project, I have had to read a little bit about linear time invariant systems. In the process of educating myself, I, of course, was introduced to the Dirac delta functional/distribution, $...
0 votes
0 answers
22 views
Find the maximum of the following function $Q(x_1, x_2, ..., x_N)$ subject to some constraints.
Given a set of non-negative real numbers $c_1, c_2, ..., c_N$, and a positive real number $D$ where $D << 1$, find an upper bound of the function: $Q(x_1, x_2, ..., x_N)$ = $\sum_{i=1}^{N}{x_i\,...
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0 answers
28 views
Average distance between all the points on 3d surface
I am trying to calculate the average distance a particle passing through a cylinder experiences. There is both a top and a bottom and the dimensions of the cylinder are known. Particles can exit any ...
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0 answers
27 views
Confusion regarding Tangent Basis
I am trying to get a better grasp of how to find the basis of the tangent space. Here is one example I worked on in hopes of practicing it: Consider the chart $(U,\psi)$, the manifold $\mathcal{M} = S^...
0 votes
1 answer
34 views
Propositional Logic - Is my simplification correct?
The problem statement is: $A \land B \land A \land (B \lor C) \lor B \land (B \lor C)$ and my solution is $ = A \land B \land A \land (B \lor C) \lor (B \land (B \lor C))$ => Now since $(B \land (...
-3 votes
1 answer
65 views
Associative laws - removal of brackets
The associative laws for addition and multiplication means (1): \begin{align*} (a + b) + c &= a + (b + c) \\ (a \cdot b) \cdot c &= a \cdot (b \cdot c) \end{align*} Does the above also ...
0 votes
1 answer
41 views
Are there infinitely many odd composite numbers with digit-disjoint factorizations?
I've been playing around with an idea about composite numbers and the digits of their factors. I've noticed a certain pattern, and for lack of a better term, I've started calling numbers that exhibit ...
0 votes
0 answers
16 views
Reference for classical action of the standard height function on the two-torus written as sum of elementary and elliptic integrals?
The height function of the two torus $\mathbb{T}^2$ is a standard example. It has $2$ hyperbolic points and $2$ elliptic points. I was wondering if there exists a reference that computes the classical ...