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 Yearling
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Mar
7
reviewed Approve another question on surds and how to use math symbols in this site
Feb
26
comment Lower bound for non-negative definite matrix
The matrix $$\left( \begin{array}{cc} 0 & 1 \\ -1 & 2 \\ \end{array} \right)$$ is non-negative definite but your expression equals $-2$. Perhaps you would like to stipulate that $A$ also be symmetric?
Feb
16
awarded  Good Answer
Jan
16
awarded  Custodian
Jan
16
reviewed Leave Open How do you find the angle between a diagonal of a cube and one of its faces?
Jan
16
reviewed Looks OK How do you find the angle between a diagonal of a cube and one of its faces?
Jan
16
reviewed Looks OK Integration Techniques - Adding [arbitrary] values to the numerator.
Jan
16
reviewed Approve Card game question
Dec
16
comment Determine the number of revolutions the normal to a curve makes as it moves along a curve in three dimensions?
That is correct, which is why I claimed your question is not well-defined! It only becomes so once you fix a pair of points on the sphere once and for all.
Dec
6
comment If $X$ is independent of $Z$ and $Y$ is dependent with $Z$ is it possible for $X + Y$ to be independent of $Z$?
@Did Thank you for pointing that out!
Dec
6
comment If $X$ is independent of $Z$ and $Y$ is dependent with $Z$ is it possible for $X + Y$ to be independent of $Z$?
If $X+Y$ is independent of $Z$ and $X$ is independent of $Z$, then $(X+Y)-X = Y$ must also be independent of $Z$.
Dec
6
comment Determine the number of revolutions the normal to a curve makes as it moves along a curve in three dimensions?
You can make this question well-defined by first restricting to curves whose normals are never zero, allowing you to define a unit normal everywhere, and assuming this unit normal is a continuous map into the unit sphere. Select two points on the unit sphere not in the image of that map. Use (say) a stereographic projection based at one of them to project the curve into the plane. Define the number of "revolutions" to be the winding number of the (projected) unit normal around the second point.
Dec
6
comment Mapping CDF's to each other
The result is false for discrete distributions. A simple example is given by two Bernoulli variables with parameters $p$ and $p'$ such that $p\ne p'$ and $p\ne 1-p'$.
Oct
25
comment How do you calculate an upper-confidence bound on a problem with 2 means?
That's right--and leave out the left endpoint of the interval altogether.
Oct
25
comment How do you calculate an upper-confidence bound on a problem with 2 means?
This is a nice exposition but it addresses a slightly different problem: the question asks for a UCL of the mean, not a symmetric CI for the mean.
Oct
24
comment Bound of Standard Normal Integral
The upper bound given by $1/\sqrt{2\pi}$ for $-1\lt z\lt 1$ and $(1/\sqrt{2\pi})|z|\exp(-z^2/2)$ otherwise is easy to integrate explicitly.
Oct
15
comment Prove that a polygon with nonnegative area is determined by at least three points.
@Sawarnik I wasn't claiming the question concerns anything other than Euclidean geometry. Pointing out that this statement is wrong in other geometries demonstrates the logical necessity of invoking some axiom that is enjoyed by Euclidean geometry.
Aug
30
comment Name for this matrix operation?
Because there are many ways to describe this operation (outer products, tensor products, etc), and it's really about a purely mathematical question, I think the math community may (a) have more interest in it and (b) be able to provide a broad and insightful collection of useful answers.
Aug
25
awarded  Yearling
Jun
19
comment Bottom to top explanation of the Mahanalobis distance?
Cross-posted at stats.stackexchange.com/questions/62092/….