2.31 Thursday, April 16, 2020

2.31.1 Top new questions this week

Raytracing; why 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 ...

asked by Tomi https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=36939 10 votes

answered by MassDefect https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=42264 18 votes

How use the black mode permanently

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219317

Now I can use this functionResourceFunction["DarkMode"][] to use the dark mode, but when I turn on Mathematica again, the black mode will not work. How can I set to use the black mode permanently.

asked by https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=71882 9 votes

answered by M.R. https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=403 5 votes

DeleteCases depending on all elements

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219412

I have a listed of Tupels

list = {{10, 5}, {20, 4}, {20, 3}, {10, 6}}; 
 
If there are two elements a and b for which 
 
a[[1]] <= b[[1]] && a[[2]] <= b[[2]] 
 
then I would like to delete  ...

asked by fravity https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=22275 8 votes

answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 7 votes

subsubsectionMathematica is unable to compute the derivative of the function \(\frac {\sin ^2(x)}x\) https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219273

Consider the function \[f: \mathbb R\to \mathbb R, x\mapsto \begin {cases}\frac {\sin ^2(x)}x, & x\neq 0, \\ 0, & x=0.\end {cases}\]

It is clear that \(f\in \mathcal C^1(\mathbb R)\) and that

asked by Maximilian Janisch https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=68670 8 votes

answered by Bob Hanlon https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=9362 12 votes

How to download "Epidemic Data for Novel Coronavirus COVID-19"

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219282

I am using Mathematica and I would like to download the dataset "Epidemic Data for Novel Coronavirus COVID-19" for basic investigation from Wolfram homepage. Can anyone give me some instructions or ...

asked by Johann Riedler https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=71867 7 votes

answered by morbo https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=48686 6 votes

NIntegrate vs quadGK in Julia

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219198

I am trying to understand the numerical integration routine by using as a benchmark the function

f[x_] := -x^2 + x^4 
 
 
used to define the following function 
 
g[z_] := NIntegrate[1/Sqrt[-f[x]], {x, z,  ... 

asked by Smerdjakov https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=55615 7 votes

answered by MassDefect https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=42264 7 votes

Overflow with NDSolve

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219593

Backslide introduced in 10.0, persisting through 12.1.

I am trying to solve the following differential equation and plot the result:

ClearAll["Global`*"] 
rin = 10^-30; 
sol = NDSolve[{Sqrt[x]  ...

asked by mattiav27 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=8822 6 votes

answered by xzczd https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=1871 2 votes

2.31.2 Greatest hits from previous weeks

What are the most common pitfalls awaiting new users?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=18393

As you may already know, Mathematica is a wonderful piece of software. However, it has a few characteristics that tend to confuse new (and sometimes not-so-new) users. That can be clearly seen from ...

asked by Dr. belisarius https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=193 459 votes

answered by Michael E2 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4999 277 votes

How to find the position of elements in a list satisfying criteria

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=180

Say I have a list x={2,4,6,8,10} and I want to find out the positions 
of the elements that are greater than 7. 
 
Select[x, #>7&] gives the elements themselves, and Position[x,8] gives the  ... 

asked by PeterR https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=140 62 votes

answered by J. M.’s technical difficulties https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=50 60 votes

How do I draw a pair of buttocks?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=66538

I’m trying to develop a function which 3D plot would have a buttocks like shape.

Several days of searching the web and a dozen my of own attempts to solve the issue have brought nothing but two ...

asked by Simpleton Jack https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=22399 287 votes

answered by mikuszefski https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=7608 440 votes

How can I plot a graph of an integral?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=78451

I want to plot the following function:

\[\int \left (\frac {\Gamma (x+1)}{2}-\frac {\Gamma (x-1)}{2}\right ) \, dx\]

asked by Anixx https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=651 3 votes

answered by k_v https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=24727 8 votes

Make a scatter plot from two lists

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=21884

I have two lists of values

xx = {0.1, 0.3, 0.35, 0.57, 0.88, 1.0} 
yy = {1.2, 3.5, 4.5, 7.8, 9.0, 12.2}

I want to make a scatter plot (list plot) with xx as x axis and yy as y axis. The help ...

asked by Patrick Li https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=2403 27 votes

answered by Eric Thewalt https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=6313 38 votes

Are you interested in purchasing David Wagner’s "Power programming with Mathematica"?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=16485

I recently contacted McGraw-Hill to see if they have a mechanism in place for printing out-of-print books that are still of interest. Specifically, I asked about "Power programming with Mathematica" ...

asked by Todd Allen https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=249 158 votes

answered by Todd Allen https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=249 232 votes

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:

PP = -(( ( Cosh[y1 ] +  Sinh[y1 ])(- Cosh[(-L +  y2) ] +  Sinh[(-L + y2) ])) 
    /(s (2   Cosh[L ]  ...

asked by max https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=796 31 votes

answered by nixeagle https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=814 50 votes

2.31.3 Can you answer these questions?

With a Large output, clicking Show all or Show more freezes Mathematica

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219430

Running the following code takes about 30 min on my laptop (everything before the Reduce is instant) and produces a Large output that Mathematica does not display, only shows buttons Show more, Show ...

asked by Sander Heinsalu https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=6211 1 vote

MathMF Error, Can’t Import VIdeo

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219195

I am getting this error HElP....

asked by Ajit Yadav https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=71840 1 vote

Best parameter for smoothing splines

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=219616

I am trying to implement a module to determine the best value for the smoothing parameter of a smoothing spline interpolation of a given dataset. To calculate the cross-validation score of a given ...

asked by Daniele Binosi https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=25023 1 vote