15,261 reputation
13087
bio website quantdec.com
location Northeastern US
age 14
visits member for 2 years, 9 months
seen Oct 18 at 15:12

Consultant (environmental and spatial stats a specialty), expert witness, and teacher. I can be reached through (outdated but still valid) links posted on my web site.

Twitter: @WilliamAHuber // ASA-P website: http://amstatphilly.org/


Why waste time learning, when ignorance is instantaneous?

--T(iger) Hobbes.

For any complex problem there is a simple solution. And it's always wrong.

--[Mis?]attributed to H.L. Mencken by Dava Sobel, Longitude.


Dec
21
comment An recurrence equation that can be solved in version 7 but not in version 8
It is interesting that the same problem, with $5$ changed to $4$, is solved in less than $0.1$ seconds with MMA 8, and with $5$ changed to $7$, the solution also takes less than $0.1$ seconds (although it's trivially expressed in terms of DifferenceRoot, which is just another way of giving up). With $5$ changed to $6$, a useful solution is obtained in $6$ seconds.
Dec
21
comment Can Depth be used as an equivalent for MatrixQ?
I confess to being mystified by this question. First, what is a "phrase," exactly? Second, if we take these to be Mathematica expressions, it is obvious they do completely different things, leaving me wondering what you might mean by "interchangeable." I am voting to close this as a non-question.
Dec
21
awarded  Nice Answer
Dec
20
comment How to calculate this sum?
There is a story, well known to mathematicians, about a very young Karl Gauss being set the problem of summing $1+2+\cdots+100$. He obtained the solution almost immediately by observing that by taking the sum from both ends, it "folds" into $(1+100)+(2+99)+\cdots+(49+52)+(50+51)$ = $101+101+\cdots+101$ = $50\times 101$. Summing $f(i/n)$ is accomplished with the same idea.
Dec
20
comment How to find lattice points on a line segment?
Nice idea. Incidentally, I noticed, in editing the question, that it stipulates the solutions should have positive coordinates.
Dec
20
revised How to find lattice points on a line segment?
deleted 1 characters in body; edited title
Dec
20
answered How to calculate this sum?
Dec
20
reviewed Close Function with different set of arguments
Dec
19
reviewed Close How to pass arguments between functions
Dec
18
reviewed Close Deformed style when exporting eps files
Dec
18
awarded  Good Answer
Dec
18
comment Edges and crossing
I wonder what crossing "over" and crossing "under" mean: how do you tell?
Dec
17
comment About extension fibonacci
The final expression needs some modifications to be correct: it must compute modulo $10$ (the length of the cycle) rather than modulo $9$ and it must offset the result by $1$, because MMA will complain when you try to index that list with a zero.
Dec
17
comment About extension fibonacci
For the purpose of identifying the $n$th *digit* in these "Fibonacci strings"--rather than just the $n$th step of their generation--it would be more convenient to represent the cycles slightly differently; namely, as $(14,45,59,91)$ and $(11,12,23,35,58,81,13,34,47,71)$.
Dec
16
answered How to draw a great circle on a sphere?
Dec
15
comment How can I express an algebraic expression as a product?
Could you please give a specific criterion, or at least an example, of what it means to write such an expression as a "product"? Because it is not a polynomial, there seems no natural way to decompose it. In fact, we could take any expression $f(x,y)$ and any other expression $g(x,y)$ and write $f$ as the product $f(x,y)=g(x,y) h(x,y)$ where $h(x,y)=f(x,y)/g(x,y)$.
Dec
14
comment How to determine the center and radius of a circle given three points in 3D?
@Daniel In an edit to my answer, I have implemented one interpretation of your suggestion. It is rather elegant in its brevity, fairly efficient, and I suspect (without extensive testing) that it is robust.
Dec
14
revised How to determine the center and radius of a circle given three points in 3D?
added 1973 characters in body
Dec
14
comment Revolution plot with 2 variable
Nothing to be sorry about, Renaud. An upvote had been reversed, which made me concerned that someone had tested out this solution, found it wanting, and then downvoted it out of frustration. It turns out to have a more mundane explanation: that user has now been removed from SE, suggesting that their actions overall might have been found to be inconsistent with norms of reasonable behavior.
Dec
14
comment Revolution plot with 2 variable
I know this is a shot in the dark, but given the recent downvote, I would be grateful to learn what could be done to improve this answer. Are there limitations worth pointing out? (Probably.) Is the exposition unclear at any point? Is there a superior alternative?