9.30.2 Greatest hits from previous weeks

9.30.2.1 Plotting a Phase Portrait

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=14160

I'm trying to plot a phase portrait for the differential equation 
$$x'' - (1 - x^2) x' + x = 0.5 \cos(1.1 t)\,.$$ 
The primes are derivatives with respect to $t$. I've reduced this second order ODE to ... 
[plotting] [differential-equations]
 

asked by covertbob https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4528 Score of 45

answered by David Slater https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=1746 Score of 41

9.30.2.2 Figuring when the minute and hour hand coincide on a clock

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=573

I would like to list all possible times in a 12-hour period, where the hour hand overlaps the minute hand completely.  This is really a question about three distinct things - to be done in Mathematica ... 
[equation-solving]
 

asked by Steve D https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=191 Score of 16

answered by Verbeia https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=8 Score of 22

9.30.2.3 Extract real part of a complex expression better than Re does

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=3306

I have a complex expression with real positive variables only. 
 
Mathematica Input Style: 
 
... 
[symbolic] [trigonometry]
 

asked by max https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=796 Score of 38

answered by nixeagle https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=814 Score of 60

9.30.2.4 How to make a spiroglyphic?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=188139

Some (older) members of this group might remember playing vinyl LP records. Recently, at the Abbey Road studio there was a spiroglyphics coloring book for sale. It looks like a nice programming ... 
[image-processing] [code-request] [generative-art]
 

asked by TheDoctor https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=2263 Score of 15

answered by b3m2a1 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=38205 Score of 20

9.30.2.5 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 Score of 21

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

9.30.2.6 What does # mean in Mathematica?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=19035

I asked Mathematica to compute the following 
 
 Solve[c (1-x)^2-x^(1/4) == 0, x] 
 
 
and it returned this: 
x = Root[#1^8 c^4 - 8 #1^7 c^4 + 28 #1^6 c^4 - 56 #1^5 c^4 ... 
[syntax] [core-language]
 

asked by ronanymous https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=5730 Score of 48

answered by Dr. belisarius https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=193 Score of 77

9.30.2.7 How to make Jacobian automatically in Mathematica

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=5790

If we have two vectors, $a$ and $b$, how can I make Jacobian matrix automatically in Mathematica? 
 
$$ a=\left( 
\begin{array}{c} 
x_1^3+2x_2^2 \\ 
3x_1^4+7x_2 
\end{array} 
\right);b=\left( 
\begin{array}{... 
[vector-calculus]
 

asked by George Mills https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=1012 Score of 41

answered by Jens https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=245 Score of 58