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visits member for 2 years, 3 months
seen Apr 16 at 18:17

Consultant (environmental stats a specialty) and teacher.


Jan
4
reviewed Close How to use the same color bar for different DensityPlot
Jan
4
comment How to get exact roots of this polynomial?
@minthao: Those roots are exact. What you seem to mean, then, is that you wish to identify some of the roots with some of the roots of another (unspecified) polynomial (which is how those cosines are defined).
Jan
4
revised How to get exact roots of this polynomial?
deleted 26 characters in body; edited title
Jan
4
comment How to get exact roots of this polynomial?
@b.gates And the next two steps are to let $x\to z/2$ to clear out powers of $2$ and then to take the big factor, $p(z)=1+3 z-3 z^2-4 z^3+z^4+z^5$ and symmetrize it via $p(z+1/z)z^5$: the primitive eleventh roots of unity pop right out.
Jan
2
comment Turn list of edges into a polygon function
@Daniel The example output is an intersection of half-planes, which can describe only a convex figure.
Jan
2
comment Turn list of edges into a polygon function
The type of example you give will work only for convex polygons. Is that a fair assumption to make in your application? If so, may we also assume the vertices have already been sorted in the order they appear around the polygon's boundary, and that the sorting follows a conventional orientation (such as keeping the interior of the polygon always to the left)? A solution for non-convex polygons can be obtained but would require more work (equivalent to triangulating them). Is it possible you only need some procedure to solve the point-in-polygon problem?
Jan
2
reviewed Leave Open Domain Coloring
Jan
2
reviewed Close Problem with SphericalPlot3D plotting
Dec
31
comment Given a time series of n samples with a known probability mass function, how can I predict the next sample?
Bruce, whether the question is migrated or reposted depends on how much it ought to change when it appears on the target site. In your case I would suggest closing it here, because you won't have a specific Mathematica question until you have a solution method, and posting a slightly different question either on stats or the signal processing site to ask about solution methods. Once you have developed a satisfactory method you could return here (if you need to) and ask more specifically about how to implement it in Mathematica.
Dec
31
comment Given a time series of n samples with a known probability mass function, how can I predict the next sample?
We would welcome a question like this over at stats but first it would have to be clarified: presumably, the prediction of the "next sample" is relying on serial correlation among the previous samples, so we would want to know what assumptions are being made about this. In general, we find it is more productive for people to describe the kinds of data they have and to state the real problems they are trying to solve, rather than asking us to provide algorithms or code for an abstractly described solution (whose appropriateness may be doubtful).
Dec
28
comment How to represent a list as a cycle
@Mr Very nice! I understand that your second method selects the lexicographically earliest representative of the class of all rotations of a list and then replaces any list by its representative. Because that is far superior in timing to the (quadratic) pattern-matching solution I posted, I'm deleting that solution.
Dec
28
comment How to visualize 3D fit
+1. It is useful at this stage to plot the residuals against the fit: that will make your comments more precise. BTW, fit["FitResiduals"] is a built-in way to obtain the residuals.
Dec
28
comment How to visualize 3D fit
A standard--and very effective--way to show the fit is to plot the residuals (equal to actual - estimated) against $x$ and $y$. For a good fit they should cluster evenly and randomly around the $xy$ plane. Because there's no question about where that plane lies, you don't even need the third dimension. For instance, many people map out the residuals in 2D using scaled and/or colored point symbols to represent their sizes and signs.
Dec
26
revised Define Log so that negative reals evaluate on lower edge of branch
added 154 characters in body
Dec
26
comment Using Transpose with a list as the second argument
+1 I am thinking the illustrations might work even better with some color coding. E.g., colors[1, 1] = Darker[Red]; colors[1, 2] = Darker[Green]; colors[1, 3] = Darker[Blue]; colors[2, 1] = Lighter[Red]; colors[2, 2] = Lighter[Green]; colors[2, 3] = Lighter[Blue]; f[x_] := Replace[MatrixForm[x], Subscript[a, i_, j_, k___] -> Style[Subscript[a, i, j, k], colors[i, j]], -1]; f[A], etc.
Dec
26
comment How do I expand a sum?
You are requesting two changes: first to Expand the products in the summation and second to Distribute the action of Sum over the addition. Consulting the help pages for Expand and Distribute will answer your question.
Dec
26
answered Define Log so that negative reals evaluate on lower edge of branch
Dec
26
reviewed Close How do the experts use the interactive notebook facilities of Mathematica?
Dec
24
revised How do I solve this equation?
Removed a potentially deceptive term from the title (this is not a functional equation).
Dec
21
comment Can Depth be used as an equivalent for MatrixQ?
@jVincent I do not know why you are addressing that last comment to me: I have not written anything here about lack of knowledge, intuition, FullForm, f[x_], or anything else you mention, nor have I ever suggested that the status of this question should be resolved based on our guesses about the O.P.'s state of mind. I have explained why I think this question, based on its merits, needs improvement, without resorting to any speculation about the knowledge or background of the person who asked it. (And--unlike 7 other people--I have not downvoted it.)