6.45 Tuesday, February 17, 2015

Tuesday, February 24, 2015

================================== Top new questions this week: ==================================

[Can Mathematica’s random number generation be improved?]http://mathematica.stackexchange.com/questions/75303/can-mathematicas-random-number-generation-be-improved

Performance on Random Number generation is intolerable. Whenever you need many deviates from the same distribution but with different parameters it takes forever.

Here is a thread on Poisson ...

- asked by JEP (11 votes), answered by JEP (4 votes)

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[The efficiency compare between Flatten[#, 1] & and Join @@ #&] http://mathematica.stackexchange.com/questions/75590/the-efficiency-compare-between-flatten-1-and-join

Err..Often I met the situation to join lists at the first level and I 
used to just Flatten[#, 1] &@ them. However, I found(when glance 
over the mathematica.stackexchange.com) someone else prefer  ...

- asked by Harry (11 votes), answered by Michael E2 (8 votes)

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[Is Mathematica ‘ContourPlot‘ function really so efficient?] http://mathematica.stackexchange.com/questions/75352/is-mathematica-contourplot-function-really-so-efficient

I wanted to find the roots of the function \(f(x,y)=\sin (3.2x)\sin (1.3y)-2.1 \sin (1.3x)\sin (3.2y)\). This is what the function looks like:

f[x_, y_] = Sin[3.2 x]*Sin[1.3*y] - 2.1*Sin[1.3*x]*Sin[3.2*y] 
...

- asked by anderstood (11 votes), answered by george2079 (16 votes)

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[How to randomly select subsets]http://mathematica.stackexchange.com/questions/75431/how-to-randomly-select-subsets

I have a list of around 300 elements. I want to sample subsets of length 25 such that my samples are all distinct. My first inclination was to use something like RandomSample[Subsets[list, 25], ...

- asked by mtiano (7 votes), answered by Mr.Wizard (8 votes)

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[Prevent Export from overwriting files]http://mathematica.stackexchange.com/questions/75745/prevent-export-from-overwriting-files

Export["filepath1",Expression1] works for me, but if filepath1 already exists, it will be overwritten. I’d like Export to notify me and ask for a confirmation, if it tries to overwrite filepath1.

I ...

- asked by user1541776 (6 votes), answered by Mr.Wizard (11 votes)

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[How trustworthy is NMaximize?]http://mathematica.stackexchange.com/questions/75668/how-trustworthy-is-nmaximize

Suppose I solve a constrained optimisation problem using NMaximize. How confident can I be of the accuracy of the result?

For concreteness, suppose that F,G are (exactly known) functions (say, ...

- asked by Feanor (6 votes), answered by mikeagibson (8 votes)

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[Mathematica and POV-Ray workflow: ListContourPlot3D]http://mathematica.stackexchange.com/questions/75497/mathematica-and-pov-ray-workflow-listcontourplot3d

I have the following function describing a molecular electronic Orbital.

f[r_] = E^-((r - R0)/\[CapitalDelta]r)^2; 
 
r = Sqrt[x^2 + y^2 + z^2]; 
cosphi[x_, y_, z_] := If[x == 0 &&  y == 0  ...

- asked by DPengel (6 votes)

================================== Greatest hits from previous weeks: ==================================

[How to generate a random snowflake]http://mathematica.stackexchange.com/questions/39361/how-to-generate-a-random-snowflake

’Tis the season... And it’s about time I posed my first question on Mathematica Stack Exchange. So, here’s an holiday quest for you Graphics (and P-Chem?) gurus.

What is your best code for generating ...

- asked by Peltio (100 votes), answered by Silvia (132 votes)

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[Where can I find examples of good Mathematica programming practice?]http://mathematica.stackexchange.com/questions/18/where-can-i-find-examples-of-good-mathematica-programming-practice

I consider myself a pretty good Mathematica programmer, but I’m always looking out for ways to either improve my way of doing things in Mathematica, or to see if there’s something nifty that I haven’t ...

- asked by J.M. (333 votes), answered by faysou (308 votes)

================================== Can you answer these? ==================================

[Precision loss in FourierDCT]http://mathematica.stackexchange.com/questions/75292/precision-loss-in-fourierdct

I have high precision data that I want to do Fourier transform with, but it looks like the precision is lost dramatically.

data = ...

- asked by xslittlegrass (2 votes)

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[Can I use Mathematica 9.0 to open an MX file produced by Mathematica 10?]http://mathematica.stackexchange.com/questions/75581/can-i-use-mathematica-9-0-to-open-an-mx-file-produced-by-mathematica-10

I have used Mathematica 10 installed on a workstation of university’s lab to run a NDSlove code that produced a .mx file. Then I copy the .mx file to my laptop which has Mathematica 9.0. When I try to ...

- asked by lxy (1 vote)

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[Is it possible to circumvent this overflow?]http://mathematica.stackexchange.com/questions/75329/is-it-possible-to-circumvent-this-overflow

I’m trying to evaluate the following function numerically:

$ 
f(A,B)=\frac{2A\pi ^{5/2} (-1)^B}{(A!)^2B!} \, 
_4\tilde{F}_3\left({\frac{1}{2},1-A,1-A,1-B\atop  ...

- asked by Ziofil (1 vote)