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bio website quantdec.com
location Northeastern US
age 14
visits member for 2 years, 6 months
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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 I can be reached through (outdated but still valid) links posted on my web site.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.


May
22
reviewed Close Forecast Future Stock Prices - Brownian Motion
May
22
reviewed Close How to estimate system recource usage of a SparseArray?
May
21
comment How can I detect an ellipse in a photo?
+1 That's a real tour de force, beautifully described. Impressive.
May
21
comment Unexpected behavior of confidence bands for data presenting two regions with uneven noise
Heteroscedasticity can be complicated: no longer does it suffice to stipulate that all residuals have the same variance, so now you need a model not only for the data values, but also an equally complicated one for the variances of their residuals. You're in the realm of highly specialized coding. If you know what you're doing, MMA is a great platform for writing that code; otherwise, look to specialized platforms like R and hope someone has contributed a model that might be appropriate for your situation.
May
21
comment Speeding up a numerical constrained quadratic optimization
@OleksandrR's suggestion to use a quadratic programming solution typically requires 0.02 seconds or less when applied to problems of the same size having random coefficients.
May
21
comment How can I detect an ellipse in a photo?
Substantial progress towards a solution can be found by reviewing these related posts. A Hough transform looks attractive.
May
20
comment Problem with the Plot of Functions and PlotLegends
What specifically is wrong with the output?
May
20
comment Solar System Orbital Parameters
Just in case you are interested in accuracy, it might be worth noting that the system of ODEs described in your previous question at mathematica.stackexchange.com/questions/25039/… is not what is usually meant by an "n-body simulation," because it does not account for interactions among the bodies: it's just a collection of independent central field solutions. It might be a fine approximation for times close to the initial time but will be observably incorrect.
May
20
comment Find all the integer numbers $a$, $b$, $c$, $d$, $e$, $f$, $k$ to this equation have three integer different solutions?
The question, which evidently is missing several words, now reads as if you are asking for all integral values of $a,\ldots,k$ in the interval $[-10,10]$ for which your equation has three distinct integral solutions. Is this a correct interpretation?
May
19
reviewed Approve suggested edit on Im trying to find the eigenvectors of an 11*11 matrix but can't get it to recognise my data
May
18
reviewed Close Generating a list of all factorizations
May
18
reviewed Leave Open Strange Behavior of NDSolve
May
18
reviewed Leave Open Doing vector manipulations on Mathematica
May
18
comment Using single replacement rule to convert algebraic expression
You might find Alternatives to be useful.
May
17
comment Solving an ODE in power series
+1 This is a good start. Power series solutions, though, are frequently used to obtain recursion equations for the coefficients (of any solution that might be analytic within a neighborhood of the point of expansion). It would be nice, then, to have a function that outputs these equations (given a differential operator as input), rather than just obtaining an approximate solution with a limited radius of accuracy. In order to analyze singular points, it would also be useful to consider slightly more general series of the form $z^\alpha(a_0+a_1z+a_2z^2+\cdots)$ for non-integral $\alpha$.
May
16
reviewed Close How to tell Mathematica to make assumptions?
May
16
reviewed Leave Open Using ImageTransformation[] with a lookup table
May
16
reviewed Close List of Tribonacci Polynomials with Mathematica?
May
15
comment Integration of a rational function
Alternatively, use the Residue Theorem. Implicitly assuming $b\gt 0$ (WLG) and $c\gt 0$, we may (very quickly) obtain the solution as 2 \[Pi] I Sum[Residue[(a + x)/((b^2 + (a + x)^2) (1 + c (a - x)^2)), {x, z}], {z, {b I - a, I/Sqrt[c] + a}}] // Simplify, yielding $\frac{2 a \sqrt{c} \pi }{1+2 b \sqrt{c}+4 a^2 c+b^2 c}$.
May
15
revised How to deal with zero in NDSolve in mathematica?
added 94 characters in body