4.11.1 Top new questions this week

4.11.1.1 How to implement a discrete data representation?

http://mathematica.stackexchange.com/questions/139818/how-to-implement-a-discrete-data-representation

 
I'm currently working with large datasets of "discrete data".  Each of these is a multiset of real numbers of the form $kS + B$, where $k$ is an integer, and $S$ (the "scale") and $B$ (the "bias") are  ...
 

- asked by kjo (17 votes), answered by gwr (14 votes)

4.11.1.2 Mathematica incorrectly giving zero for partial derivative

http://mathematica.stackexchange.com/questions/139669/mathematica-incorrectly-giving-zero-for-partial-derivative

 
Bug introduced in 9.0.1 or earlier 
 
 
 
Mathematica is incorrectly reporting that the partial derivative of a certain expression is zero. 
 
I try to compute the following: 
 
D[SymmetricPolynomial[3, {x1,  ...
 

- asked by Izaak Meckler (17 votes), answered by march (6 votes)

4.11.1.3 Finding vampire numbers

http://mathematica.stackexchange.com/questions/139808/finding-vampire-numbers

 
How to find vampire numbers by using Mathematica? 
 
 
A number $v=xy$  with an even number $n$ of digits formed by multiplying a pair of $n/2$-digit numbers (where the digits are taken from the  ...
 

- asked by vito (13 votes), answered by wolfies (8 votes)

4.11.1.4 Why do subsequent evaluations seem to be stopped by a False Condition (/;)?

http://mathematica.stackexchange.com/questions/139461/why-do-subsequent-evaluations-seem-to-be-stopped-by-a-false-condition

 
Exploring another problem and this example of @halirutan, I came across an evaluation behavior I don't understand. 
 
When g[] below is evaluated the first time, ig[] is evaluated and a message printed;  ...
 

- asked by Michael E2 (12 votes), answered by Carl Woll (13 votes)

4.11.1.5 Bug? Numerical calculation error with FullSimplify and arbitrary precision

http://mathematica.stackexchange.com/questions/139697/bug-numerical-calculation-error-with-fullsimplify-and-arbitrary-precision

 
Bug introduced after 5.2, fixed in 8.0, reintroduced in 9.0 and persisting through 11.0.1 
 
 
 
Is this a bug? 
 
If I do 
 
FullSimplify[n E^(0``10 n)] 
 
 
then it returns 
 
n/2 
 
 
what is obviously incorrect. 
 
...
 

- asked by David Bevan 10votes

4.11.1.6 Is there a convention on which name to use for a throwaway variable? (Like underscore in Python)

http://mathematica.stackexchange.com/questions/139622/is-there-a-convention-on-which-name-to-use-for-a-throwaway-variable-like-under

 
I would prefer to write {_, foo} = LongFunctionName[arg1, arg2] instead of foo = LongFunctionName[arg1, arg2][[2]] or foo = Last @ LongFunctionName[arg1, arg2]. Using an actual name for the throwaway  ...
 

- asked by ZeitPolizei (10 votes), answered by Mr.Wizard (5 votes)

4.11.1.7 Extract images from large avi movies (50-100 GB)

http://mathematica.stackexchange.com/questions/139819/extract-images-from-large-avi-movies-50-100-gb

 
I will get large RGB avi files (35 Hz, 1600*1200 pixels) of up to 100 GB size. All three channels contain the same grayscale image. 
 
I want to extract each avi file into one channel png images. 
 
To do  ...
 

- asked by mrz (8 votes), answered by mrz (11 votes)