Mathematica Weekly Newsletter
Mathematica Weekly Newsletter

Top new questions this week:

A quicker than outer

I need to get a matrix $\{a(x_i-x_j)\}$, where $x_i$ form a partition of an interval, $a(x)$ is a given function. I use In[67]:= a[x_?NumericQ] := N[Exp[-Abs[x]]]; x = Table[-10 + 0.02 (j - ...

list-manipulation matrix performance-tuning  
asked by Dmitri 11 votes
answered by Szabolcs 14 votes

Pick elements from list "separately"

I have the following list I want to pick elements from: mylist = {1, 5, 7, 3, 4, 7, 2, 9, 9, 1, 10, 12, 2, 64, 34, 64} I have another list with 0's and 1's which is my selector: selector = {1, 1, ...

asked by holistic 10 votes
answered by eldo 9 votes

How to take and evaluate a specific part of a list without evaluating the rest?

I have a large list, for example, lis = {x + y, x y, Sin[x] y + Exp[y], x^2 y} and its elements depend on variables x and y. Later I assign numerical values to x and y x = {1, 2, 3, 4, 5} y = {3, ...

list-manipulation evaluation  
asked by renphysics 10 votes
answered by Chris Degnen 9 votes

Wiggly and imprecise animated gif output

Trying to make animated gif of zooming into famous Ford circles. With the code visibleQ[lh_, hr_, c_, k_] := Which[ lh >= 1/(2 k), If[2 c k^2 <= 1 && lh^2 < c (1 - c k^2), True, ...

graphics performance-tuning animation  
asked by მამუკა ჯიბლაძე 9 votes

How to extract a region shape from an 2 colour image?

I'll start by saying that I don't know anything about image processing. I have an image and I need to extract its outermost shape for use in a WordCloud. The image only has two colours and the ...

graphics image-processing word-cloud  
asked by Edmund 9 votes
answered by nikie 4 votes

Create new notebook at fixed size

Using Ctrl+n we are effectively doing FrontEndTokenExecute["New"] and, at least on Windows, new window has WindowSize equal to current Input/Selected Notebook's WindowSize. Can Ctrl+n produce a ...

front-end notebooks options customization  
asked by Kuba 9 votes
answered by Kuba 9 votes

Automatically adjust Russia on the map (Mathematica 10.0)

Bug introduced in 10.0.0 and fixed in 10.1 I'm using Mathematica 10.0 on Windows 10. If I take a map of any country (even continent), it automatically adjusts the size of the map. ...

bugs geography  
asked by garej 9 votes
answered by ybeltukov 14 votes

Greatest hits from previous weeks:

1 Plot, 2 Scale/Axis

I would like to plot those two datasets on top of each other. But they have very different range on the $y$ axis. How can I have two different axis? I found the following on the help menu but quite ...

asked by 500 93 votes
answered by ArgentoSapiens 87 votes

3D surface that looks like a virus

I have been recently using Mathematica for composing animations that are part of the supplementary information of my papers. I am currently trying to build an animation that involves a viral ...

graphics animation code-request  
asked by user2098 16 votes
answered by Chris Degnen 18 votes

Can you answer these?

Calculating in the group ring $Q[GL_n(Z)]$

I am trying to use Mathematica to check some identities in the group ring $Q[GL_n(Z)]$. Is there a package/function of Mathematica to do this? Thanks a lot in advance!

matrix group-theory  
asked by Mike 1 vote

Mysterious Difference in Equation Formulation for NDSolveValue and NDEigensystem

I have taken a standard equation from Mathematica help from here for a stress operator. I have also formulated the equivalent equations from engineering texts. When I compare the two equations Using ...

differential-equations formatting  
asked by Hugh 2 votes

WhenEvent behavior changed from v9 to v10 - how to fix the code?

A couple of years ago I asked a question about solving n-body systems with NDSolve and detecting collisions with WhenEvent. I received an excellent answer, but unfortunately that code does not work ...

differential-equations numerical-integration version-10  
asked by shrx 2 votes
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