6.31.2 Greatest hits from previous weeks

6.31.2.1 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

6.31.2.2 Generate a Unit Circle Trigonometry

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=2456

Struggling often with Trigonometry I would like to have some code to generate this Unit Circle Trigonometry. Would be of great help when I need to transform some data : 
[graphics] [trigonometry]
 

asked by 500 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=172 18 votes

answered by Mark McClure https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=36 32 votes

6.31.2.3 Drawing a square root spiral

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=66969

Here is a start. I'm looking for a nice way to draw it. 
 
... 
[graphics] [geometry]
 

asked by matrix89 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=5379 24 votes

answered by Bob Hanlon https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=9362 21 votes

6.31.2.4 How do I make a 3DPlot using cylindrical coordinates?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=19076

I'm trying to plot a function of the form $z(r,\theta)$ where $r \in [0, R]$ for a finite R, $\theta \in [0,2\pi[$, and z is the third coordinate, a function of the first two. I couldn't find anything ... 
[plotting]
 

asked by Learning is a mess https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=5643 18 votes

answered by whuber https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=91 24 votes

6.31.2.5 How to calculate contour integrals with Mathematica?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=34073

How to calculate the integral of $\frac{1}{\sqrt{4 z^2 + 4 z + 3}}$ over the unit circle counterclockwise for each branch of the integrand? 
[calculus-and-analysis] [complex]
 

asked by user64494 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=7152 42 votes

answered by Artes https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=184 64 votes

6.31.2.6 Skip header lines on import

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=50718

When importing a data file what are the comment symbols for Mathematica? 
That is, given a file like this 
 
 blabla 
bulbul 
 
1 2 6 54 7 ... 
.. 
 
 
what symbol do I have ... 
[import] [text]
 

asked by MaxJ https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=14687 20 votes

answered by george2079 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=2079 18 votes

6.31.2.7 Using Export[] sends the file where?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=8586

I am trying to use the  Export  command to convert a list of plots into a *.gif file, and the command runs and executes well, but I can't find the file! Where is it ... 
[export]
 

asked by Patrick Da Silva https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=1785 37 votes

answered by Vitaliy Kaurov https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=13 51 votes