2.8.1 Top new questions this week

2.8.1.1 Terrifying performance decrease for contour/density plots in v10.1 -> 10.3

http://mathematica.stackexchange.com/questions/99255/terrifying-performance-decrease-for-contour-density-plots-in-v10-1-10-3

 
I setup for download a test dataset athttp://www.inrim.it/~magni/cm.dat.gz (a set of 64800 triplets x,y,z). 
 
The behavior can be reproduced with the following code: 
 
link =  ...
 

- asked by alessandro (24 votes), answered by Jason B (13 votes)

2.8.1.2 Cyclic Take function?

http://mathematica.stackexchange.com/questions/99188/cyclic-take-function

 
Is there some direct and simple "cyclic Take", sometimes also known as "overtake" in Mathematica. That is, if the take specification runs out of elements, it just cycles back to the beginning (as many  ...
 

- asked by murray (21 votes), answered by kglr (22 votes)

2.8.1.3 Speeding up generation of block diagonal matrix

http://mathematica.stackexchange.com/questions/99467/speeding-up-generation-of-block-diagonal-matrix

 
I'm struggling with the following problem. I have $48$ square matrices (full, filled with real machine precision numbers, thus are packed, all different) of size $128$. I wolud like to place them on a  ...
 

- asked by mmal (16 votes), answered by ybeltukov (14 votes)

2.8.1.4 Integrate returns imaginary answer for smooth, real function

http://mathematica.stackexchange.com/questions/99395/integrate-returns-imaginary-answer-for-smooth-real-function

 
Bug introduced in 7 or earlier and persisting through 10.3 
 
 
 
I'm trying to evaluate the integral: 
 
$$\int_0^{\infty} \frac{1}{4 b \sqrt{\pi} r} e^{-(b-r)^2}(e^{4 b r} - 1) \mathrm{d}r$$ 
 
with  ...
 

- asked by Kevin Driscoll 15votes

2.8.1.5 Detecting an ellipse in a glaucoma photo

http://mathematica.stackexchange.com/questions/99578/detecting-an-ellipse-in-a-glaucoma-photo

 
For glaucoma diagnosis it is common to determine a "cup to disk ratio" which compares the diameter of the optic disk (VDD) and optic cup (VCD). The optical disk is visible as a circular red feature  ...
 

- asked by indra ginanjar A.T (14 votes), answered by belisarius has settled (17 votes)

2.8.1.6 How to implement the general array broadcasting method from NumPy?

http://mathematica.stackexchange.com/questions/99171/how-to-implement-the-general-array-broadcasting-method-from-numpy

 
A friend of mine introduced array broadcasting in the Python NumPy package which is very convenient (and also highly efficient). 
 
The idea is perfectly shown in this picture: 
 
 
 
Basically, the method  ...
 

- asked by matheorem (14 votes), answered by Pillsy (15 votes)

2.8.1.7 Derivative of a pure function with SlotSequence

http://mathematica.stackexchange.com/questions/99439/derivative-of-a-pure-function-with-slotsequence

 
I can live with this but I can't figure out why the following is 0: 
 
Derivative[1][f[##] &][x] 
 
 
 
0 
 
 
From documentation for Derivative: 
 
 
[...] Whenever Derivative[n][f] is generated, the WL  ...
 

- asked by Kuba (14 votes), answered by Michael E2 (13 votes)