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bio website quantdec.com
location Northeastern US
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visits member for 2 years, 7 months
seen Aug 27 at 19:17

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 I can be reached through (outdated but still valid) links posted on my web site.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.


Feb
28
reviewed Leave Open How can I control the number format of exported data?
Feb
28
comment Showing a rectangular plot on an almost-closed sphere
This is on the right track, but the example does not seem mathematically correct, because it illustrates a series of maps from the plane to the sphere rather than a single, fixed map to the sphere. In fact, it appears to be a series of maps from the square to the sphere which, in the limit, will map only the square to the entire sphere. A mathematically correct answer would look like the texture on the sphere is fixed (immobile) and that the sphere is merely being more or less chopped off near its top.
Feb
27
comment Showing a rectangular plot on an almost-closed sphere
Thanks, Steve. I wasn't sure, because under a stereographic projection those axes won't look like the one in your image: there has to be a huge amount of distortion in the northern hemisphere to accommodate all the numbers between $2$ and $\infty$ in size :-).
Feb
27
comment Showing a rectangular plot on an almost-closed sphere
I answered before you added that image, Steve. But what precisely do you mean by "actual axes" on the surface of the sphere? What values do they purport to show? Explain that and perhaps we can find a solution that meets your needs :-).
Feb
27
comment Eigenvalues and Determinant of a large matrix
It makes sense only to evaluate this determinant relative to the determinant of $m$. When you divide DET by Det[m] you will get values around $10^{-13}$ down to $10^{-16}$ in size, indicating that only one to four decimals of accuracy have actually been lost out of the original $17$. In other words, DET is just the opposite of a "huge number": it is extremely small, relative to a natural measure of numerical size for this problem.
Feb
27
comment Showing a rectangular plot on an almost-closed sphere
@Daniel That's right. The importance of stereographic projection is that it is a rational transformation between the affine and projective planes, so that changing the pole of the projection--which I think is what you might have in mind with "affine slices"--just gives an alternative affine picture of the same cubic (or the same rational function, if you began with a rational function).
Feb
27
comment Mathematica vs Sigmaplot (Non LinearModelFit)
@rc Constant error variance is assumed by (unweighted) least-squares fitting. When that variance changes, intuitively it makes sense to put less weight on the points with larger variance--and in fact using appropriately weighted least squares is one way to fix up the procedure. But there are great advantages to re-expressing the data to produce constant error variances: interpretation is simpler, prediction is simpler and more reliable, and in physical applications often the re-expressions have meaning. These issues are extensively discussed on stats.stackexchange.com, Mary.
Feb
27
comment Mathematica vs Sigmaplot (Non LinearModelFit)
Unless you are confident the error variance is constant across different values of $x$, you should instead be fitting the model $\log(y) = \log(a_0) + a_1 t + a_2 t^2$. Use LinearModelFit; it's fast, easy, and can output a huge amount of additional information.
Feb
27
answered Showing a rectangular plot on an almost-closed sphere
Feb
26
comment Confirming the existence of a function related to a matrix
The requirements on $f$ imply $m_{ij} + m_{ji}$ = $f(i,j)+f(j,i)$ = $2f(i,j)$, giving a unique solution--as well as a formula for it--if any solution exists at all.
Feb
26
revised How can I get the solution of complicated implicit function?
added 654 characters in body
Feb
26
answered How can I get the solution of complicated implicit function?
Feb
25
comment Extracting a single layer from a SHP file
@belisarius I cannot explain why that is. I agree with the OP that the documentation is (at best) incomplete--confusing is more like it--but I can reaffirm with great confidence my assertion about the lack of a "layer" structure in shapefiles. There is an authoritative, comprehensive specification available at esri.com/library/whitepapers/pdfs/shapefile.pdf. Possibly the OP did not actually use the command given in the question; possibly "file.shp" is actually the name of a directory! One clue is the appearance of "theme1": that's a temp shapefile dumped into the same directory.
Feb
25
comment Extracting a single layer from a SHP file
Shapefiles do not have layers. Perhaps you are importing an entire directory or archive of shapefiles (a "SHP bundle")? In this case the layer names correspond to the individual shapefiles, which only have to be specifically named to be separately imported.
Feb
25
revised Plotting many tables in a single plot
edited title
Feb
25
comment How to remove redundant {} from a nested list of lists?
Your example following "At this point' makes no sense, because expressions like (t,c) have no meaning, nor do expressions enclosed in square brackets. Otherwise, it appears you are asking to apply a replacement rule like //. {a_List->a} to your expressions. Is that what you're looking for?
Feb
22
revised Problems with doing calculus on Interpolating functions
added 14 characters in body; edited title
Feb
22
comment Subdividing a polygon , equivalent fractions
Have you noticed that subdividing the perimeter into equal-length segments does not subdivide the area into equal-area pieces? This distinction seems of great importance in the intended application of visualizing fractions!
Feb
21
comment How Simplify and Assume can be combined on matrix products?
I don't see anything in your code that stipulates the $C_i$ "must be considered as matrices," so I doubt Mathematica can tell, either. Except for mind readers, that makes your question just as difficult for people to interpret as it is for MMA. Perhaps, to make this question interpretable and answerable, you could state--in mathematical or at least English terms, rather than non-working code--what it is you're trying to do and what you need to accomplish.
Feb
21
awarded  Nice Answer