# All Questions

100,979 questions
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### Mean sphere in hyperbolic 3-space

What would be the natural equivalent of the notion of a mean sphere at a point of a smooth surface when the surface no longer lives in the Euclidean 3-space but in the hyperbolic 3-space ?
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### Example of non accessible model categories

By curiosity, I would like to see an example of a model category with the underlying category locally presentable which is not accessible in this sense (and just in case: even by using Vopěnka's ...
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### Do manifolds inherit topological proporties of their models?

Suppose a space is for example paracompact, then a manifold that modeled on it is paracompact? It seems that it is true but how we can show it. More general questions what topological properties ...
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### State of art of hyperfunction theory in solving partial differential equations

What are the advantages of 'representing distribution(or more generalized functions) as boundary value of holomorphic functions', and their use in solving pde?
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### Quasinilpotent vectors of Newton potential vanish

Suppose $\Omega$ is a smooth bounded domain in $\mathbb{R}^3$. Consider the Newton potential $$T [\phi](x) = \int_{\Omega} \frac{1}{|x-y|} \phi(y)dy.$$ It is well know ...
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Consider the set of all discrete functions from $\mathbb F_q^2$ to $\mathbb F_q$ (denote it by $\mathcal F(\mathbb F_q^2, \mathbb F_q)$, the cardinality $|\mathcal F(\mathbb F_q^2, \mathbb F_q)| = q^{... 0answers 59 views ### Linear Morphism of Schemes Let$U$be an arbitrary scheme and we consider the schematic fiber product$\mathbb{A}^1 _U = \mathbb{A}^1 _{\mathbb{Z}} \times_{\mathbb{Z}} U$. My question referer to Bosch's "linear morphisms" (of ... 0answers 46 views ### Fully faithful functor from schemes to spaces Is there a fully faithful functor from the category of schemes to the category of topological spaces and continuous maps (or some other sufficiently topological objects, e.g. smooth manifolds and ... 0answers 78 views ###$\infty$-categorical understanding of Bridgeland stability conditions? On triangulated categories we have a notion of Bridgeland stability conditions. Is there any known notion of "derived stability conditions" on a stable$\infty$category$C$such that they become ... 0answers 18 views ### how to calculate the reflection matrix between two planes? [on hold] the equation of plane A is 9x+2y+3z-10=0, plane B is z=0. The question is how to calculate the reflection matrix of these two planes. The motivation of this question is to transform the curve in space ... 2answers 34 views ### Rate of convergence for eigendecomposition Consider the discrete Dirichlet Laplacian on a set of cardinality$n.$For example the Dirichlet Laplacian$\Delta_D$on a set of cardinaltity 4 is the matrix $$\Delta_D := \left( \begin{matrix} 2 &... 0answers 21 views ### Understanding Partial Derivatives of a Neural Network I have to compute the following double derivative:$$ \partial _{x_i} \nabla_W \sigma(f(W,x))$$where$W = (W_1, W_2, \dots, W_L)$is the set of weight matrices,$f(W,x)$is a$linear$neural ... 0answers 23 views ### Functorial cones This is probably more a reference request than a real question. I was studying dg-categories in order to understand how one can derive a functorial cone construction when a triangulated category (... 0answers 30 views ### Ok is a principal ideal domain if and only if [on hold] Let k be an algebraic number field.Show that Ok is a principal ideal domain if and only if it satisfies the following condition: for every α in k but not in Ok,there are β,γ in Ok such that 0<|norm(... 0answers 23 views ### Approximation of functions by tensor products Given a function$f(x,y)\in L^p(R^d;L^\infty(B_R))$with$1<p<\infty$, where$B_R:=\{y\in R^d: |y|\le R\}$, can we find a sequence of functions$f_n$of the form$f_n(x,y)=\sum_{i=1}^ng_i(x)h_i(...

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