tracing – Recovery of the limit points of the concave shell (or alpha form) in 3D

I am trying to find the limit points of a 3D concave region which is described by a list of points. If the region was convex, I would take the convex shell and simply extract the coordinates from it.

However, since the shape is concave, I have to use an alternative algorithm. For example, I can implement alpha forms as proposed in

DelaunayMesh in a specified closed region – creating a concave hull from a set of points


Find a concave shell.

I can successfully get a MeshRegion object that represents the shape I want. However, unlike the convex shell, required implementations such as Delauney triangulation or the code offered in produces a MeshRegion which always contains all the points. It simply selects the triangles to include, but it retains the internal triangles. So, I cannot easily choose only the points which are at the border. I have tried to apply RegionBoundary which works for 2D shapes but when applied to 3D mesh it acts as an identity for some reason.

Examples of data:

pts = Join(RandomPoint(Cuboid({0, 0, 0}, {1, 1, 1}), 1000), 
   RandomPoint(Cuboid({1, 0, 0}, {2, 0.5, 0.5}), 1000));

I want to get only those points at the limit of the form (reject the points inside).

adb – The SHELL command works well as a standalone command, but fails when placed in a shell script?

Android 8.1 PIXEL 2 with root access.

I have already seen this question here, but the only solution did not help me at all. I will try to make this as simple as possible for the example.

If i run the following command in the terminal emulator or adb shell:

am force-stop com.myapp.frustrated

It will exit the app very well. But when I run it in this shell script:

am force-stop com.myapp.frustrated

Nothing is happening. It's strange to me that I can do many other commands just fine in a script, but a handful of them don't work.

Any suggestions you have are greatly appreciated.

shell – Write a script to add an eth0 interface to the S7 edge

can anyone take a look at this script? I want to add it to an sh file. When I connect my Ethernet adapter, I don't want to enter all the commands again. I just want to run it from the shell. Is it correct?

ip link set eth0 up
sleep 1;
ip addr add dev eth0
sleep 1;
ip route add default via dev eth0
sleep 1;
ndc network create 1
sleep 1;
ndc network interface add 1 eth0
sleep 1;
ndc resolver setnetdns 1
sleep 1;
ndc network default set 1

Scheduling a LaunchAgent shell task on macOS Catalina

I have created a .plist file at:


Which contains:


This script works well if I use:
sh /Users/_USER_/Developer/ from a terminal, however, it does not seem to work automatically at 15 m after midnight. How could I make it work?

How to suppress XFS file system warning in mongodb shell?

Whenever I start a mongodb shell, I get this annoying warning:

Server has startup warnings:
2020-02-01T08:54:27.220+0100 I  STORAGE  [initandlisten]
2020-02-01T08:54:27.220+0100 I  STORAGE  [initandlisten] ** WARNING: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine
2020-02-01T08:54:27.220+0100 I  STORAGE  [initandlisten] **          See

I understand that in some environments this is useful. But in my particular case, I am using mongodb on a VPS server which has a preinstalled ext4 file system. There is no option to change this. And it's not necessary anyway – in this particular application, there are no performance issues and there never will be. The server is already under control for this application.

I was browsing the documentation to find a command line option to suppress this warning message, but there is none. Or maybe there is one, but I did not find it?

python3 – How NOT to change the shell prompt when activating a python venv?

I created a venv like this:

python3 -m venv .venv

When I activate it, the shell prompt is changed.

antkong@konga-mbp ~/dev/my-project (git-branch-name)
$ source .venv/bin/activate
(.venv) konga-mbp:my-project antkong$

How can I keep the prompts the same?

What is the convex shell of the quaternion symmetries of the three-dimensional cube?

It is well known that there are exactly five regular three-dimensional convex polyhedra, called Platonic solids.
In 1852 the Swiss mathematician Ludwig Schlafli discovered that there were exactly six regular 4 convex polytopes (the generalization of
4-dimensional polyhedra) and that, for dimensions 5 and above, there are only three!

The six 4 regular polytopes are:

NAME                    VERTEXES   EDGES   FACES  CELLS
Hypertetrahedron              5      10      10      5
Hypercube                    16      32      24      8
Hyperoctahedron               8      24      32     16
24-cell                      24      96      96     24
Hyperdodecahedron           600    1200     720    120
Hypericosahedron            120     720    1200    600

The simplest to describe are the first two:
a model for the hypertetrahedron can be obtained as the convex shell of the canonical base in $ mathbb R ^ 5 $ (hence a
4-dimensional object), while a model for the hypercube is the Cartesian product $ (0, 1) times (0, 1) times (0, 1) times (0,
1) $

As in the case of 3 dimensions, the dual of a regular 4-polytope is also a regular 4-polytope and it turns out that the regular six
The 4-polytopes found by Schlafli are linked to each other via duality as follows.

Hypetetrahedron    <->   Itself
24-cell            <->   Itself
Hypercube          <->   Hyperoctahedron
Hyperdodecahedron  <->   Hypericosahedron

This means that it is enough to describe the 24 cells and the hypericosahedron to be all known. In other words:

Hypertetrahedron    =  convex hull of the canonical basis in 5 dimensions
Hypercube           =  (0,1)x(0,1)x(0,1)x(0,1)
Hyperoctahedron     =  dual of the hypercube
Hyperdodecahedron   =  dual of the hypericosahedron
24-cell                ???
Hypericosahedron       ???

The description of the last two 4-polytopes above can be obtained by considering the quaternions $ mathbb Q $.
visualization $ mathbb R ^ 3 $ in $ mathbb Q $ via the card
$$ (x, y, z) mapsto xi + yj + zk, $$
it is well known that each quaternion
$ q $, with $ Green q Green = 1 $, give a rotation $ R_q $ sure $ mathbb R ^ 3 $ via the formula
R_q (v) = qvq ^ {- 1}, quad forall v in mathbb R ^ 3.

In fact the correspondence $ q mapsto R_q $ is a double coating of $ N / A (3) $ by the unitary sphere $ mathbb Q $.

leasing $ P_ {20} $ be the icosahedron $ mathbb R ^ 3 $, Take into account quaternionic symmetries of $ P_ {20} $, which I will write as
$ mathbb {QS} (P_ {20}) $, defined as the
set of all unitary quaternions $ q $ such as $ R_q $ leaves $ P_ {20} $
invariant. In symbols
mathbb {QS} (P_ {20}) = {q in mathbb Q: Vert q Vert = 1, R_q (P_ {20}) = P_ {20} }.

Well, the convex shell of $ mathbb {QS} (P_ {20}) $ in $ mathbb R ^ 4 $ proves to be a model for the hypericosahedron!

Since the symmetries of a regular polyhedron are the same as the symmetries of its dual, it is clear that the symmetries
of $ P_ {12} $, the dodecahedron, is nothing new: the convex shell of $ mathbb {QS} (P_ {12}) $ is just another model for the

Go to the tetrahedron (double auto), call it $ P_4 $, the convex shell of $ mathbb {QS} (P_ {4}) $ give a model for the
4 remaining polytopes, namely the 24 cells, completing the description of the six 4 Schlafli polytopes.

Question: What is the convex shell of the quaternion symmetries of the 3-dimensional cube?

If I am not mistaken, this polytope 4 has 48 vertices and 144 edges, so it is not in Schlafli's list and therefore cannot be regular.

root access – Individual commands work fine, but shell script generates errors

I am trying to create a shell script to configure iptables and add some routes to my device running Android 10. I have root access.

Here is the script. I called him

iptables -t filter -F FORWARD
iptables -t nat -F POSTROUTING
iptables -t filter -I FORWARD -j ACCEPT
iptables -t nat -I POSTROUTING -j MASQUERADE
ip rule add from lookup 61
ip route add default dev tun0 scope link table 61
ip route add dev wlan1 scope link table 61
ip route add broadcast dev wlan1 scope link table 61

sysctl -w net.ipv6.conf.wlan1.disable_ipv6=1

I have a root console open via ADB, and I can execute each individual command from the script manually in the console, as follows:

enter description of image here

… etc.

But this happens when I run my script:

enter the preformatted text here

and I don't really understand why.

I have limited skills with Android and Linux, so I tried to follow and combine a few examples, but I was unlucky.

linux – Shell starts in edit mode only. No prompt appears, no command can be executed

My tcsh appears in a weird way. Whether as a login shell or in a terminal, it now always starts with a simple cursor. I can type text in the terminal but that's all I can do. No prompts appear, no linked keys work, nothing.

Help with this problem?

How to block to open Web Shell in my CentOS 6

I am currently using mod_security in combination with maldec and blocking almost all attempts to download shells, which leads to error 406. However, I have found a "problem" if I download Shell via an ftp client, then I can use shell in the hosting. my question is how to block the opening of the shell even if it is downloaded via ftp? any mod_security rule to use and if so what? I also use cPanel