6.29.2 Greatest hits from previous weeks

6.29.2.1 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. 
 
... 
[list-manipulation]
 

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

6.29.2.2 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)\... 
[functions] [calculus-and-analysis]
 

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

6.29.2.3 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 
... 
[numerics] [language-design]
 

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

6.29.2.4 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 ... 
[performance-tuning] [regions] [geometry]
 

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

6.29.2.5 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.... 
[warning-messages] [syntax] [debugging] [faq]
 

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

6.29.2.6 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, ... 
[machine-learning] [date-and-time] [neural-networks]
 

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

6.29.2.7 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 ... 
[geometry] [image3d]
 

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