2.5 Thursday, November 19, 2020

2.5.1 Top new questions this week

3D Inclusion with structured mesh and coarse and arbitrary matrix

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234780

I am wondering if there is a simple way to define a structured 3D mesh (inclusion) like e.g. that and surround it with a corse and unstructured Matrix. It should be possible to refine both more or ...

asked by Max https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=68812 15 votes

answered by Tim Laska https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=61809 8 votes

Smoother jelly / water effect on an image

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234653

I’m trying to achieve a jelly / water surface effect. I’d like it to be a bit smoother. Here I am taking a triangulated rectangle and perturbing all points by a little random noise for each frame. ...

asked by flinty https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72682 14 votes

answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 15 votes

Can Mathematica be used to edit MP3 tags?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234564

Can Mathematica edit mp3 tags? I have a set of files and I’d like to batch process artist, album title, etc. I know other tools exist; I wonder if Mathematica can do it.

asked by GregH https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4393 11 votes

answered by flinty https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72682 15 votes

How can I put the edge of a rectangle inside it rather than outside it?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234866

Problem: when I draw a rectangle and put a coloured edge around it, the displayed edge is centred along the nominal edge and if it follows the same course as one of the axes then it does not show up. ...

asked by ruffle https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=59886 7 votes

answered by Brett Champion https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=69 5 votes

How do I invert my matrix?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234836

I have the following matrix \(M\):

\begin{bmatrix} 
P & p & 0 & 0 \\ 
pe_1 & Pe_1 & \sqrt{P^2 - p^2}q_1 & \sqrt{P^2 - p^2}r_1 \\ 
pe_2 & Pe_2 & \sqrt{P^2 - p^2}q_2 & 
\end{bmatrix}

asked by Anson Bdo https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=75764 7 votes

answered by LouisB https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=22158 14 votes

How to convert a Dataset into an indexed dataset / association-of-associations given a column header?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234931

Given a dataset as such

If "letter" is the header that is chosen, how do I convert it into an indexed dataset / association-of-associations? i.e. How do ...

asked by IntroductionToProbability https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=60568 6 votes

answered by Anton Antonov https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=34008 6 votes

Automatically draw chords from n-1 points on a circle to a fixed point on the circle

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234729

I want to put n equally spaced points on a circle and automatically draw chords from all points to a fixed point preferably P(0,0). I have managed to draw the points and the circle so far with

asked by Guy Foxx https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=75736 6 votes

answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 5 votes

2.5.2 Greatest hits from previous weeks

How to find the position of elements in a list satisfying criteria

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=180

Say I have a list x={2,4,6,8,10} and I want to find out the positions of the elements that are greater than 7.

asked by PeterR https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=140 67 votes

answered by J. M.’s discontentment https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=50 63 votes

Finding Limits in several variables

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=21544

Is there a way to find a limit of a multivariable function, like

\[\lim _{(x,y)\to (0,0)} f(x,y)\] with Mathematica?

When \(f\) is continuous, we can use \[\lim _{(x,y)\to (0,0)} f(x,y)=\lim _{(x,0)}\]

asked by Dominic Michaelis https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=5899 31 votes

answered by whuber https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=91 42 votes

Why round to even integers?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=2116

According to the Mathematica help:

Round rounds numbers of the form x.5 toward the nearest even integer.

For example:

Round[{0.5, 1.5, 2.5, 3.5, 4.5}]

gives

asked by wxffles https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=427 82 votes

answered by Per Alexandersson https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=488 50 votes

Why is raytracing so slow?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219629

I’m trying to get some rays to bounce in a circle. But I want to be able to control the reflections, i.e. the direction the rays bounce in the circle. I have a MWE below, and it is severely limited by ...

asked by Tomi https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=36939 31 votes

answered by Tim Laska https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=61809 42 votes

How do I identify the source of a "Tag times protected" error?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=11982

I have some code that looks like

Table[ 
    a = 1; 
    b = {2, 3} 
    c = i;, 
    {i, 2} 
]

which gives an error:   Set::write: Tag Times in c {2,3} is Protected....

asked by dearN https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=204 29 votes

answered by Mr.Wizard https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=121 35 votes

Mathematica command that allows it to read my intentions

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=194384

In version 2.0 of Mathematica there was a command, ReadProgrammerIntentions[ ] which allowed it rapidly compose code that could solve problems simple to complex, ...

asked by MikeY https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=47314 52 votes

answered by MarcoB https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=27951 38 votes

How to make a Spherical Cow?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=125043

Being a theoretical physicist, I always have a great respect for Spherical Cow. So I thought about making one myself. I am not sure how can I create (something considered to be the simplest!) this ...

asked by Sumit https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=8070 69 votes

answered by andre314 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=5467 76 votes

2.5.3 -Can you answer these questions?

Setting pieces of "matrices" - unwanted behavior

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234703

I am constructing matrices whose elements are lists themselves (of varying length), and am (re)setting the entries of these matrices using among others the "All" command. It seems that in ...

asked by Stijn https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=69486 2 votes

system of coupled nonlinear pdes with FEM (magneto-hydrodynamic mass transfer)

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234749

I’m trying to reproduce the magneto-hydrodynamic flow studied here using the nonlinear FEM functionality, and have been having trouble implementing the Neumann boundary conditions. Pardon the long ...

asked by George Varnavides https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=41179 1 vote

Create a Cellular Automata rule in Mathematica

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=234577

I want to create an image in a cellular automata, more specifically an image of an object, like a turtle for example. I found this article online, and i am trying to replicate the results for growing ...

asked by Joana Bugalho https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=75694 2 votes