5.22 Tuesday, August 2, 2016

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Top new questions this week: 
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[How can I detect locations of Go (aka Baduk, Weiqi) stones on a board?] http://mathematica.stackexchange.com/questions/121835/how-can-i-detect-locations-of-go-aka-baduk-weiqi-stones-on-a-board

The Goal

There are a couple apps that score a Go board from a photo. I was wondering if something like that would be possible with Mathematica. The key step is to detect the positions of the stones ...

- asked by Mark S. (19 votes), answered by halirutan (2 votes)

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[What are all the "magic" Symbols in the Mathematica language?] http://mathematica.stackexchange.com/questions/121981/what-are-all-the-magic-symbols-in-the-mathematica-language

Leonid Shifrin once wrote (excerpted):

(Unevaluated) is one of a very few "magic symbols", along with Sequence and Evaluate - these are deeply wired into the system and can not be easily ...

- asked by Mr.Wizard (16 votes), answered by Mr.Wizard (9 votes)

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[What has changed in pattern matching functions with the Orderless attribute?] http://mathematica.stackexchange.com/questions/121564/what-has-changed-in-pattern-matching-functions-with-the-orderless-attribute

In making an attempt to answer this question, we ran into a version-dependent pattern-matching issue. An extended discussion in the comments transpired, and some inconsistencies arose. Consider the ...

- asked by march (16 votes)

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[Converting a Sierpinski tetrahedron to a Graph] http://mathematica.stackexchange.com/questions/121553/converting-a-sierpinski-tetrahedron-to-a-graph

I need a representation of a 3D Sierpinski gasket as a graph to perform some simulations on. The 2D version is included in GraphData[], but the 3D one is nowhere to be found, so I was wondering if ...

- asked by FEARxxx (13 votes), answered by J. M. (2 votes)

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[Working with DynamicModule: SetDelayed + OwnValues] http://mathematica.stackexchange.com/questions/121584/working-with-dynamicmodule-setdelayed-ownvalues

Shortly, definitions in form of e.g. x:= RandomReal[] have to be avoided 
inside DynamicModule[{x}, ...]. Why?, this Prints immediately: 
 
DynamicModule[{x}, x := Print[1]; {}]

It hit us hard in the ...

- asked by Kuba (12 votes), answered by Kuba (13 votes)

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[How to speed up pattern matching] http://mathematica.stackexchange.com/questions/121911/how-to-speed-up-pattern-matching

Main Problem

Mr.Wizard posed this question when discussing another problem.

I reproduce the main part of Mr.Wizard’s problem here:

MatchQ[{1, 2, 3, 4, 5}, {x__?((Echo[##]; False) &), y__}]

On ...

- asked by Wjx (11 votes), answered by Michael E2 (5 votes)

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[How to efficiently implement k-FN (k-Furthest Neighbors)?] http://mathematica.stackexchange.com/questions/121541/how-to-efficiently-implement-k-fn-k-furthest-neighbors

I’d like to pick k points from a set of points in n-dimensions that are approximately "maximally apart" (sum of pairwise distances is almost maxed). What is an efficient way to do this in MMA? Using ...

- asked by M.R. (10 votes), answered by C. Woods (2 votes)

================================== Greatest hits from previous weeks: ==================================

[Writing a word with straight lines] http://mathematica.stackexchange.com/questions/113403/writing-a-word-with-straight-lines

Here is an interesting way to write a word: (it is from a poster for the International Museum Day 2006; I believe it even won an award at an international design competition)

by Boris Ljubicic. ...

- asked by VividD (70 votes), answered by Anton Antonov (32 votes)

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[Make a beautiful Moiré effect] http://mathematica.stackexchange.com/questions/112998/make-a-beautiful-moir%c3%a9-effect

How do I make the following Moiré pattern?

I tried:

A = Plot[Table[n, {n, 1, 30}], {x, 0, 31}, 
GridLines -> {Table[n, {n, 1, 30}], None}, 
GridLinesStyle -> AbsoluteThickness[1.2],  ...

- asked by vito (23 votes), answered by gpap (34 votes)

================================== Can you answer these? ==================================

[Looking for a package for finite mappings] http://mathematica.stackexchange.com/questions/121776/looking-for-a-package-for-finite-mappings

I am looking for a package for dealing with "mappings" \(f\colon A\to B\) where \(A\) and \(B\) are finite subsets of the set of all possible (inert) expressions.

I need operations like:

Computing \(f(a)\) ...

- asked by masterxilo (3 votes)

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[Using Palettes in Mathematica Online] http://mathematica.stackexchange.com/questions/121935/using-palettes-in-mathematica-online

my student is using the online version of Mathematica for my class; it appears to not have a palette feature for typing formatted input? This was kind of shocking to me; why wouldn’t there be a ...

- asked by Jake Mirra (1 vote)

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[Derivation of an interpolation function with multiple arguments] http://mathematica.stackexchange.com/questions/121599/derivation-of-an-interpolation-function-with-multiple-arguments

I have the following interpolation function:

f[x_,a_,b_]:=70 s[a,b][[1,1,2]][x] 
 
 
where s[a,b] is the solution of a differential equation. 
 
s[a_, b_] := NDSolve[{ 
   H2[x] == Rx[x]^2 + G[x, a, b], 
   ...

- asked by Maria (2 votes)