5.47 Tuesday, February 9, 2016

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Top new questions this week: 
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[Partitioning a list when the cumulative sum exceeds 1] http://mathematica.stackexchange.com/questions/105792/partitioning-a-list-when-the-cumulative-sum-exceeds-1

I have a long list of say 1 million Uniform(0,1) random numbers, such as:

 dat = {0.71, 0.685, 0.16, 0.82, 0.73, 0.44, 0.89, 0.02, 0.47, 0.65}

I want to partition this list whenever the cumulative ...

- asked by wolfies (15 votes), answered by Mr.Wizard (18 votes)

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[How to extract a contour line (or a region) from a ContourPlot?] http://mathematica.stackexchange.com/questions/105750/how-to-extract-a-contour-line-or-a-region-from-a-contourplot

Given a ContourPlot with a set of contours, say, this:

is it possible to get the contours separating domains with the different colors in the form of lists?

For example, how to extract the ...

- asked by Alexei Boulbitch (12 votes), answered by Michael E2 (7 votes)

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[Using NDSolve to find particle trajectory] http://mathematica.stackexchange.com/questions/105859/using-ndsolve-to-find-particle-trajectory

I’m trying to simulate a particle in an electric and magnetic fields, but numerically instead of analytically. This is basically solving the equation

\[q \cdot \left (p'\times B\right ) + q\cdot E = m \]

- asked by triplebig (11 votes), answered by Sjoerd C. de Vries (11 votes)

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[why MatchQ is fast and Replace slow?] http://mathematica.stackexchange.com/questions/105626/why-matchq-is-fast-and-replace-slow

Consider a large expression, say a polynomial with 25 terms

expr=Product[Unique["a"],{i,1,25}];

to which you apply the following replacement rule:

rep={x_ f[y_] /; FreeQ[x, y] -> 0};

Since f ...

- asked by M. Tissier (11 votes), answered by Mr.Wizard (13 votes)

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[Use of some functions of the Developer Utility Package, such as BesselSimplify] http://mathematica.stackexchange.com/questions/105643/use-of-some-functions-of-the-developer-utility-package-such-as-besselsimplify

The Developer Utilities Package contains several functions that look interesting:

BesselSimplify 
GammaSimplify 
PolyGammaSimplify 
ZetaSimplify 
PolyLogSimplify 
and TrigToRadicals

However for each ...

- asked by Alexei Boulbitch (10 votes), answered by Jens (5 votes)

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[Plot of \(sin(x^x)\) is missing from \(x=143\)] http://mathematica.stackexchange.com/questions/105774/plot-of-sinxx-is-missing-from-x-143

When plotting the graph of \(\sin (x^x)\) I noticed that there is no plot from about \(x=143\). I don’t suppose there is a purely mathematical explanation for this?

So, why is there no graph in ...

- asked by Imre Vegh (10 votes), answered by MarcoB (22 votes)

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[Brackets around each item in matrix] http://mathematica.stackexchange.com/questions/105864/brackets-around-each-item-in-matrix

I have a matrix where every item in the matrix has its own brackets that I do not want. How can I remove the brackets around each item?

- asked by C. Tamaro (8 votes), answered by John Conor Cosnett (9 votes)

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

[How do I clear all user defined symbols?] http://mathematica.stackexchange.com/questions/850/how-do-i-clear-all-user-defined-symbols

Is there some way to do this other than going to Evaluation -> Quit kernel and firing a new one up?

- asked by niklasfi (37 votes), answered by Artes (31 votes)

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[Drawing a square root spiral] http://mathematica.stackexchange.com/questions/66969/drawing-a-square-root-spiral

Here is a start. I’m looking for a nice way to draw it.

Graphics[{EdgeForm[Black], White, 
  Polygon @ {{0, 0}, {-1, 0}, 
    Sqrt[2] {Cos[#], Sin[#]} &[Pi - (ArcCot[1])]}, 
  Polygon @ {{0,  ...

- asked by mathe (22 votes), answered by Bob Hanlon (17 votes)

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

[Weird behaviour for a vector InterpolatingFunction inside an NDSolve] http://mathematica.stackexchange.com/questions/105594/weird-behaviour-for-a-vector-interpolatingfunction-inside-an-ndsolve

I have run into some weird behaviour on the part of NDSolve which I find pretty bizarre and which I would like to understand better.

Suppose, for the sake of argument, that I want to study the ODE ...

- asked by Emilio Pisanty (3 votes)

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[NDeigensystem returns error due to mesh discretization when calculating vibrations of a cantilever] http://mathematica.stackexchange.com/questions/105840/ndeigensystem-returns-error-due-to-mesh-discretization-when-calculating-vibratio

There was an transcription error in the code I provided in a previous post:

NDeigensystem returns complex non-hermitian error for the calculation of vibrations of a cantilever

This resulted in it ...

- asked by user37299 (2 votes)

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[WhenEvent and Resetting of Variable in PDE when operation succeeds] http://mathematica.stackexchange.com/questions/105781/whenevent-and-resetting-of-variable-in-pde-when-operation-succeeds

I have had success in using WhenEvent to reset or change a variable within NDSolve with ordinary differential equations. My working, functioning MWE is:

Clear[usol, u, t, x, \[Lambda]] 
usol = NDSolveValue[ 
 ...

- asked by drN (3 votes)