Paul Mesnilgrente

Install rbenv and use it

2018-05-03T00:00:00+00:00

I. What is rbenv

Rbenv is a tool to manage your ruby versions. It works in collaboration with bundler which manage your development libraries versions. You can find more information on their github page.

II. Why I prefer rbenv to RVM

One reason can be found in the article on RVM: there is a bug. But actually, rbenv themselves are explaining it well here. The main reason is that I don’t like to change my shell (RVM overrides cd!) only to have a ruby version manager. I think it is an overkill in comparison of rbenv and this is dangerous as well.

Another point is, python has used the same mechanism as Ruby, the project is called pyenv. So it will be very easy to understand how pyenv works if you have understood how rbenv works. Even if python includes the concept of virtual environemnts.

III. Install and use rbenv

III.1. Install rbenv

Rbenv provides an installation script which include a plugin to facilitate the ruby installation. You can find the repository on github. To summarize it in a bash script:

# prepare the installation to avoid warnings from rbenv-doctor
curl -fsSL https://github.com/rbenv/rbenv-installer/raw/master/bin/rbenv-installer | bash
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
echo 'eval "$(rbenv init -)"' >> ~/.bashrc
# if you want to be sure that rbenv is correctly installed:
#     - close the terminal and open a new one, or
#     - source your ~/.bashrc
#     - check that everything is OK in the result of the following command:
curl -fsSL https://github.com/rbenv/rbenv-installer/raw/master/bin/rbenv-doctor | bash

III.2. Use rbenv to install ruby

When you wan to install Ruby on your OS, you have the choice. You can install ruby from your package manager (sudo apt install ruby), rbenv will take it into account. Or you can install a specific ruby version (for development maybe) with: rbenv install 2.4.2.

After installing a new version with rbenv, you should execute rbenv rehash to install/update the shims in your new version. More information about shims here.

III.3. Use rbenv to develop your jekyll website

One powerfull feature of rbenv is to set default (global) and local ruby versions easily. For example, if you want to let your default ruby version to be the one installed by the package manager, run rbenv global system. But if you want to develop your jekyll website and make it work on github, you will need to:

set a ruby version for the development
manage jekyll dependencies

Here is a script to retrieve your jekyll website, install everything and begin to write articles:

# install the currently ruby version supported by github-pages
rbenv install 2.5.3
rbenv rehash
# retrieve your website
git clone git@github.com:/user/project.github.io
# set your ruby environment to 2.4.2 in this folder
cd project.github.io
rbenv local 2.5.3
# install bundler, the ruby library package manager
gem install bundler
bundle install --path vendor
# add vendor to .gitignore if not already done
[ `grep -c vendor .gitignore` -eq 0 ] && echo vendor >> .gitignore
# star the jekyll built-in server
bundle exec jekyll serve
# if you want to show the drafts
bundle exec jekyll serve --drafts

Note: You should update your packages versions in Gemfile to make it match the one from github-pages. You can check github-pages package versions here.

Sources

RVM and Ruby installation

2018-05-02T00:00:00+00:00

Basic installation

As stated on the RVM website. You can find the following instructions here:

# install prerequisites
sudo apt install software-properties-common
# add the PPA
sudo apt-add-repository -y ppa:rael-gc/rvm
sudo apt install rvm

Note: you don’t need to update the package list because adding a PPA does it automatically in Ubuntu 18.04.

The webpage says that you should add all the user that are going to use RVM to the rvm group. Normally, sudo apt install rvm did it for your current user. You can check it by typing groups $USER. If you want to add another user, you can do it with this command: sudo usermod -a -G rvm <username>

The website says as well to change the configuration of your terminal by “Running command as a login shell”. This is under “Edit - Preferences - Command”:

Then you need to log off and log in again in order to make some changes of your environment effective. You can restart as well instead of log off and log in.

Post installation instructions

I highly recommend, once the installation are done, to install the latest stable ruby using rvm. To do so: ruby install 2.5.1, you can check the version number here.

Bug:

If by mistake, you installed another version and you don’t figure out how to make your desired ruby version the default (in my case, ruby --default use 2.5.1 didn’t work), you can put this line at the end of ~/.profile: source $(rvm 1.9.3 do rvm env --path). I had to add rvm_silence_path_mismatch_check_flag=1 to my ~/.rvmrc as well to get rid of a warning.

Note: If you see what I have done wrong, you can drop me a comment and I will update the article :)

Manage your ruby versions

To install a ruby version: ruby install 2.5.1
To make it default: ruby --default use 2.5.1

Why I use sublime text

2018-02-21T00:00:00+00:00

Sublime text is a rich text editor that can turn into a real IDE in a few minutes. Its most powerfull feature is the package control which enables plugin installation very easily. I present here my favourites plugins.

Table Editor

I use Table editor for writing Markdown. It implements some very usefull formating in your markdown tables. You can pass from:

| Column 1 | Column 2 |
|-|-|
| First line | First line second column |

to this:

|  Column 1  |         Column 2         |
|------------|--------------------------|
| First line | First line second column |

simply by pressing enter. But this is not the only feature that there is. I hardly recommend to check its documentation.

PHP-Twig

As a Symfony programmer, I am quite used to write Twig templates. And for this, nothing is better than this plugin. It does the syntax highlighting and it adds some usefull snippets. For example, you can type simply b<tab> and it will complete with {% block ... %}{% endblock %}.

PHP-Twig is the plugin that you must have if you are front-end developper in Symfony or other PHP project using this template engine.

LESS

LESS is a simple syntax highlighter for the well known less syntax. Even if I tend to use Sass these days, the package is still installed! I have some projects that were using bootstrap 3.4 and it still compiles with the less npm package.

Sass

Sass is a syntax highlither for Sass files. It even has a support for CSS 4! At least, they have an active development.

Markdown Preview

MarkdownPreview is compatible with MathJax. For example, you can type:

Inline formula \(x = 2 \times x + 10\) for example

Here is a block formula:

$$x = 2.x + 10$$

And it will render:

Inline formula $x = 2 \times x + 10$ for example

Here is a block formula:

\[x = 2.x + 10\]

Installation script

2018-02-15T00:00:00+00:00

I use this script after setting up my terminal on a fresh installation. It installs all the basics things that I usually need on my Ubuntu. It removes all the useless softwares as well (as amazon plugins).

NOTE: You may find some scripts that you know. This is probably because it is part of my scripts that you can find here or from any other thing that is setup in setup_terminal.sh.

#!/bin/bash

set -e

function require_action {
    log.py -l ERROR "${1}"
    printf "Press enter to continue... "
    read y
}

sudo apt install -y python python-pip python3 python3-pip

log.py -l ERROR 'Removing useless packages'
sudo apt autoremove --purge -y unity-webapps-common totem shotwell shotwell-common

log.py 'Adding sublime text ppa'
sudo apt install -y apt-transport-https
wget -qO - https://download.sublimetext.com/sublimehq-pub.gpg | sudo apt-key add -
echo "deb https://download.sublimetext.com/ apt/stable/" | sudo tee /etc/apt/sources.list.d/sublime-text.list

# log.py 'Adding oracle java ppa'
# sudo add-apt-repository -y ppa:webupd8team/java

log.py 'Adding nextcloud ppa'
sudo add-apt-repository -y ppa:nextcloud-devs/client

log.py 'Adding darktable ppa'
sudo add-apt-repository -y ppa:pmjdebruijn/darktable-release

log.py 'Adding Telegram ppa'
sudo add-apt-repository -y ppa:atareao/telegram

log.py 'Adding LibreOffice ppa'
sudo add-apt-repository -y ppa:libreoffice/ppa

log.py 'Adding NodeJS ppa'
curl -sL https://deb.nodesource.com/setup_8.x | sudo -E bash -

log.py 'Update and upgrade packages'
sudo apt update && sudo apt -y upgrade

log.py 'Install basic softwares and libraries'
    # oracle-java8-installer \
sudo apt install -y nautilus-dropbox \
    easytag vim tree ttf-mscorefonts-installer \
    vlc gimp xournal gnome-chess grisbi gparted \
    libreoffice-java-common \
    git sublime-text nextcloud-client \
    nextcloud-client-nautilus curl libgnome2-bin \
    darktable python-pygments telegram \
    php mysql-server php-mysql php-xml php-intl nodejs

log.py 'Installing composer'
install_composer.sh

log.py 'Installing symfony'
sudo curl -LsS https://symfony.com/installer -o /usr/local/bin/symfony
sudo chmod a+x /usr/local/bin/symfony

log.py 'Installing NPM'
sudo npm install npm -g
sudo chown -R $USER:$(id -gn $USER) $HOME/.config
sudo npm install less -g

log.py 'Installing Messenger'
wget 'https://updates.messengerfordesktop.com/download/linux/latest/beta?arch=amd64&pkg=deb' \
 -O messenger.deb
sudo apt install -y ./messenger.deb
rm messenger.deb

log.py 'Installing Whatsapp'
log.py -l ERROR 'Nothing working without installing google chrome'

log.py 'Installing Skype'
wget 'https://go.skype.com/skypeforlinux-64.deb'
sudo apt install -y ./skypeforlinux-64.deb
rm skypeforlinux-64.deb

log.py 'Installing Slack'
wget 'https://downloads.slack-edge.com/linux_releases/slack-desktop-3.0.5-amd64.deb'
sudo apt install -y ./slack-desktop-3.0.5-amd64.deb
rm slack-desktop-3.0.5-amd64.deb

require_action 'System :
    - Install languages
    - Modify the background
    - Add workspaces
    - Install proprietary softwares (e.g):
        - Intel microcode,
        - NVidia drivers
    - Put sleep mode to never'

require_action 'Mozilla thunderbird :
    - Add email accounts
    - Install extensions :
        - Lightning, 
        - Enigmail,
        - CardBook.'

require_action 'Mozilla firefox :
    - Install lastpass,
    - Remove bookmarks,
    - Synchro firefox,
    - Go on https://startpage.com/ and set it up,
    - Add starpage as default search engine,
    - Remove other search engines,
    - Configure wallabag,
    - Add the bookmark toolbar,
    - Enable "use autoscrolling",
    - Add the search bar,
    - Configure vertical bar.'

require_action 'Sublime text :
    - Install the package control (one click in sublime),
    - Install markdown preview, LESS.'

require_action 'Install language tools.'

require_action 'Launch and configure Nextcloud.'

[ -f examples.desktop ] && rm -rf examples.desktop
[ -d Templates ] && rm -rf Templates
[ -d Public ] && rm -rf Public
[ ! -f ~/.hidden ] && echo bin >> ~/.hidden
[ `grep -c '^bin$' ~/.hidden` -eq 0 ] && echo bin >> ~/.hidden

require_action "End of the script."

Forward kinematic equations of a PRPRR

2018-01-15T00:00:00+00:00

Forward kinematics refers to the use of the kinematic equations of a robot to compute the position of the end-effector from specified values for the joint parameters.

1. Preferential jacobian calculation

(a) Calculation of $p, i, j$

n = number of links = 5
p = integer part of (n / 2) = 2
i = p + 1 = 3
j = p

(b) Calculations of $z_{k(j)}$

Formula# : $z_{k(j)} = R_{kj}.O_kO_j(j)$

$z_{1(2)} = R_{12}.\begin{pmatrix}0 & 0 & 1\end{pmatrix}^T$
$z_{2(2)} = R_{22}.\begin{pmatrix}0 & 0 & 1\end{pmatrix}^T$
$z_{3(2)} = R_{32}.\begin{pmatrix}0 & 0 & 1\end{pmatrix}^T$
$z_{4(2)} = R_{42}.\begin{pmatrix}0 & 0 & 1\end{pmatrix}^T$
$z_{5(2)} = R_{52}.\begin{pmatrix}0 & 0 & 1\end{pmatrix}^T$

$R_{12} = \begin{pmatrix} c2 & -s2 & 0 \newline s2 & c2 & 0 \newline 0 & 0 & 1 \end{pmatrix}$

$R_{22} = \begin{pmatrix} 1 & 0 & 0\newline 0 & 1 & 0\newline 0 & 0 & 1 \end{pmatrix} \rightarrow$ no rotation

$R_{32} = R_{23}^{-1} = R_{23}^T = \begin{pmatrix} 1 & 0 & 0\newline 0 & 0 & -1\newline 0 & 1 & 0 \end{pmatrix}$

$R_{42} = R_{43}.R_{32} = R_{34}^T.R_{32} = \begin{pmatrix} c4 & 0 & s4\newline s4 & 0 & c4\newline 0 & -1 & 0 \end{pmatrix}. \begin{pmatrix} 1 & 0 & 0\newline 0 & 0 & -1\newline 0 & 1 & 0 \end{pmatrix}$

$R_{42} = \begin{pmatrix} c4 & s4 & 0\newline s4 & c4 & 0\newline 0 & 0 & 1 \end{pmatrix}$

$R_{52} = R_{54}.R_{43} = R_{45}^T.R_{42} = \begin{pmatrix} c5 & 0 & -s5\newline -s5 & 0 & -c5\newline 0 & 1 & 0 \end{pmatrix}. \begin{pmatrix} c4 & s4 & 0\newline s4 & c4 & 0\newline 0 & 0 & 1 \end{pmatrix}$

$R_{52} = \begin{pmatrix} c4.c5 & c5.s4 & -s5\newline -c4.s5 & -s4.s5 & -c5\newline s4 & c4 & 0 \end{pmatrix}$

$z_{1(2)} = \begin{pmatrix}0 & 0 & 1\end{pmatrix}^T$

$z_{2(2)} = \begin{pmatrix}0 & 0 & 1\end{pmatrix}^T$

$z_{3(2)} = \begin{pmatrix}0 & 0 & 0\end{pmatrix}^T$

$z_{4(2)} = \begin{pmatrix}0 & 0 & 1\end{pmatrix}^T$

$z_{5(2)} = \begin{pmatrix}-s5 & -c5 & 1\end{pmatrix}^T$

(c) Calculations of $p_{ki(j)}$

Formula# : $p_{ki(j)} = O_kO_i(j)$

$O_1O_3(2) = O_1O_2(2) + O_2O_3(2) = 0 + \begin{pmatrix}0 & q3 & 0\end{pmatrix}^T$

$O_2O_3(2) = \begin{pmatrix}0 & q3 & 0\end{pmatrix}^T$

$O_3O_3(2) = \begin{pmatrix}0 & 0 & 0\end{pmatrix}^T$

$O_4O_3(2) = \begin{pmatrix}0 & 0 & 0\end{pmatrix}^T$

$O_5O_3(2) = \begin{pmatrix}0 & 0 & 0\end{pmatrix}^T$

(d) Calculations of $z_{k(j)} \land p_{ki(j)}$

Formula# : $\begin{pmatrix}a \newline b \newline c\end{pmatrix} \land \begin{pmatrix}d \newline e \newline f\end{pmatrix} = \begin{pmatrix} b.f - c.e\newline c.d - a.f\newline a.e - b.d \end{pmatrix}$

$z_{1(2)} \land p_{13(2)} = \begin{pmatrix}0 \newline 0 \newline 1\end{pmatrix} \land \begin{pmatrix}0 \newline q3 \newline 0\end{pmatrix} = \begin{pmatrix} -q3\newline 0\newline 0 \end{pmatrix}$

$z_{2(2)} \land p_{23(2)} = \begin{pmatrix}0 \newline 0 \newline 1\end{pmatrix} \land \begin{pmatrix}0 \newline q3 \newline 0\end{pmatrix} = \begin{pmatrix} -q3\newline 0\newline 0 \end{pmatrix}$

$z_{3(2)} \land p_{33(2)} = \begin{pmatrix}0 \newline 0 \newline 0\end{pmatrix} \land \begin{pmatrix}0 \newline 0 \newline 0\end{pmatrix} = \begin{pmatrix} 0\newline 0\newline 0 \end{pmatrix}$

$z_{4(2)} \land p_{43(2)} = \begin{pmatrix}0 \newline 0 \newline 1\end{pmatrix} \land \begin{pmatrix}0 \newline 0 \newline 0\end{pmatrix} = \begin{pmatrix} 0\newline 0\newline 0 \end{pmatrix}$

$z_{5(2)} \land p_{53(2)} = \begin{pmatrix}-s5 \newline -c5 \newline 1\end{pmatrix} \land \begin{pmatrix}0 \newline 0 \newline 0\end{pmatrix} = \begin{pmatrix} 0\newline 0\newline 0 \end{pmatrix}$

Writing of the preferential jacobian

Formula# : $J_{i(j)} = \begin{pmatrix} \sigma_1.z_1 + \bar{\sigma_1}.z_{1(j)}\land p_{1i(j)} & \dots & \sigma_n.z_{n(j)} + \bar{\sigma_{n(j)}}.z_{n(j)}\land p_{ni(j)} \newline \bar{\sigma_1}.z_{1(j)} & \dots & \bar{\sigma_n}.z_{n(j)} \end{pmatrix}$

Simplification with the nature link knowledge.

\[\begin{align} J_{3(2)} &= \begin{pmatrix} z_{1(2)}\land p_{13(2)} & z_{2(2)}\land p_{23(2)} & z_{3(2)} & z_{4(2)}\land p_{43(2)} & z_{5(2)}\land p_{53(2)}\newline z_{1(2)} & z_{2(2)} & O_{3\times1} & z_{4(2)} & z_{5(2)} \end{pmatrix}\newline &= \begin{pmatrix} -q3 & -q3 & 0 & 0 & 0\newline 0 & 0 & 0 & 0 & 0\newline 0 & 0 & 0 & 0 & 0\newline 0 & 0 & 0 & 0 & -s5\newline 0 & 0 & 0 & 0 & -c5\newline 1 & 1 & 0 & 1 & 1 \end{pmatrix} \end{align}\]

2. Calculations of $\hat{P}_{in(j)}$ by the vector $p_{in(j)}$

Formula# : $\hat{P}_{in(j)} = \begin{pmatrix} 0 & -z & y\newline z & 0 & -x\newline -y & x & 0 \end{pmatrix}$ avec $p_{in(j)} = \begin{pmatrix}x & y & z\end{pmatrix}^T$

$p_{35(2)} = \begin{pmatrix}0\newline0\newline0\end{pmatrix}$ so $\hat{P}_{in(j)} = O_{3\times3}$

3. Calculations of $dp_{(0)}$ and $d\varphi_{(0)}$

Formula# : $\begin{pmatrix}dp_{(0)} \newline d\varphi_{(0)}\end{pmatrix} = \begin{pmatrix} R_{03} & O_{33}\newline O_{33} & R_{03} \end{pmatrix}. \begin{pmatrix} I_{33} & -\hat{P}_{in(j)}\newline O_{33} & I_{33} \end{pmatrix}.J_{3(2)}.dq$ avec $dq = \begin{pmatrix}dq1 \newline \vdots \newline dqn\end{pmatrix}$

or $\hat{P}_{in(j)} = O_{3\times3}$ so $\begin{pmatrix}dp_{(0)} \newline d\varphi_{(0)}\end{pmatrix} = \begin{pmatrix} R_{03} & O_{33}\newline O_{33} & R_{03} \end{pmatrix}.J_{3(2)}.dq$

$R_{03} = R_{12}.R_{23}.R_{34} = \begin{pmatrix} 1 & 0 & 0\newline 0 & 1 & 0\newline 0 & 0 & 1 \end{pmatrix}. \begin{pmatrix} c2 & -s2 & 0 \newline s2 & c2 & 0 \newline 0 & 0 & 1 \end{pmatrix}. \begin{pmatrix} 1 & 0 & 0\newline 0 & 0 & 1\newline 0 & -1 & 0 \end{pmatrix} = \begin{pmatrix} c2 & 0 & -s2\newline s2 & 0 & c2\newline 0 & -1 & 0 \end{pmatrix}$

\[\begin{align} \begin{pmatrix}dp\_{(0)} \newline d\varphi\_{(0)}\end{pmatrix} &= \begin{pmatrix} c2 & 0 & -s2 & 0 & 0 & 0\newline s2 & 0 & c2 & 0 & 0 & 0\newline 0 & -1 & 0 & 0 & 0 & 0\newline 0 & 0 & 0 & c2 & 0 & -s2\newline 0 & 0 & 0 & s2 & 0 & c2\newline 0 & 0 & 0 & 0 & -1 & 0 \end{pmatrix}. \begin{pmatrix} -q3 & -q3 & 0 & 0 & 0\newline 0 & 0 & 0 & 0 & 0\newline 0 & 0 & 0 & 0 & 0\newline 0 & 0 & 0 & 0 & -s5\newline 0 & 0 & 0 & 0 & -c5\newline 1 & 1 & 0 & 1 & 1 \end{pmatrix}. \begin{pmatrix} dq1\newline dq2\newline dq3\newline dq4\newline dq5 \end{pmatrix}\newline &= \begin{pmatrix} - c2.dq1.q3 - c2.dq2.q3\newline - dq1.q3.s2 - dq2.q3.s2\newline 0\newline - dq1.s2 - dq2.s2 - dq4.s2 - dq5.(s2 + c2.s5)\newline c2.dq1 + c2.dq2 + c2.dq4 + dq5.(c2 - s2.s5)\newline c5.dq5 \end{pmatrix} \end{align}\]