Tagged Questions

0
votes
0answers
52 views

Triangular bounding volumes

I've come up with an alternative for beziers that might be easier to ray-trace, perhaps even though a plain vertex shader. Though I'm missing a function there. I need to find the …
3
votes
1answer
166 views

Simplifying the definition of a geometric context using sieves?

On Pages 1-3 of Cours 2 of Toën's Master Course on Stacks, he defines the notion of a Geometric context with a rather extensive list of axioms (they take up about two pages over an …
2
votes
1answer
126 views

Routh’s theorem in three dimensions

The most well known case of Routh's triangle theorem is: If the sides BC, CA,and AB are trisected at the points D, E, and F, respectively, then the area of the inside triangle for …
-2
votes
0answers
158 views

selcetive school practice question seems to have 2 answers [closed]

is a tent like shape a rectangular based prism or a triangular based prism. need answer before 17th of march 2010 (befor 16th for america)
7
votes
1answer
138 views

Stable Tables on Fluctuating Floors

If a four-legged, rectangular table is rickety, it can nearly always be stabilised just by turning it a little. This is very useful in everyday life! Of course it relies on the flo …
10
votes
2answers
301 views

Sheaves and bundles in differential geometry

Because the theory of sheaves is a functorial theory, it has been adopted in algebraic geometry (both using the functor of points approach and the locally ringed space approach) as …
9
votes
4answers
265 views

When do two holonomy maps determine flat bundles that are isomorphic as just bundles (w/o regard to the flat connections)?

Suppose we have a surface S (although the question might make as much sense in higher dimensions) and a topological group G. The data of a flat vector bundle on S (up to isomorphis …
5
votes
0answers
133 views

Prescribing Gaussian curvature

Let $K(r)$ be the piecewise function                        &nbs …
9
votes
3answers
227 views

Tetrahedra with prescribed face angles

I am looking for an analogue for the following 2 dimensional fact: Given 3 angles $\alpha,\beta,\gamma\in (0;\pi)$ there is always a triangle with these prescribed angles. It is s …
1
vote
1answer
79 views

How to compute the number of regular spheres needed to fill a rectangular space

Computing the volume of a sphere is straightforward 4/3*pi*R^3 As is the volume of a rectangular space length*width*height (e.g. 10*10*6) How might I go about determining how man …
16
votes
3answers
1k views

Perimeter/Area of finite union of unitsquares \le 4?

Prove that if H is the union of a finite number of unit squares in the plane, then the ratio of the perimeter and the area of their union is at most four. Remarks. If the squares …
6
votes
3answers
287 views

Set of vectors separated by at least a specified angle

Suppose theta and d are given. How big can a set of d-dimensional vectors be such that no pair of them are at angle less than theta? I particularly want an upper bound; that is, …
0
votes
1answer
154 views

completeness axiom for the real numbers

Do any treatises on real analysis take the following as the basic completeness axiom for the reals? "Let $A$ and $B$ be set of real numbers such that (a) every real number is eith …
8
votes
2answers
192 views

Geometrically interpreting the answer to a vector calculus question involving tangent line segments to ellipses.

Let E be an ellipse centered at the origin on the x, y plane with major radius b and minor radius a. The length of the shortest line segment tangent to E that begins on the x-axis …
2
votes
2answers
318 views

Is ellipse on a sphere convex? (proof)

Is 'small enough' ellipse projected on a surface of a sphere convex? By ellipse I mean a set of points 'C' with a constant sum |AC| + |BC|, A and B are the centers. By 'small enoug …

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