Scientific Computing

Pledge by major Python science packages to use Python 3.

Guide to partial automatic Python 3 code update.

Detailed opinion on switching to Python 3

Fine-grained OS Detection from Python script: windows_linux_detect.py

This standalone Python script has Boolean properties:

self.cygwin
self.wsl
self.linux

self.windows

self.mac

self.bsd

Matlab and Octave are popular for machine learning prototypes due to their easier to learn (vs. R) interface. Python via scikit-learn is also a top choice for machine learning. Here’s how to install LibSVM for Matlab and GNU Octave.

Prereqs:

apt install make git g++

Compile LibSVM

git clone https://github.com/cjlin1/libsvm

cd libsvm

make

Creates executables svm-train svm-predict svm-scale. Compile the Matlab/Octave and Python modules, for which the API is similar.

Compile LibSVM Matlab/Octave module

cd libsvm/matlab

Open Matlab or Octave, and from that internal Terminal, type (this uses make.m)

make

which creates a few .mex files. See the matlab/README for examples of using LibSVM from Matlab and Octave.

Compile LibSVM Python module

cd libsvm/python

make

See the python/README for examples of using LibSVM from Python.

The authors estimate about 75% of PMTK3 is available from Octave, while Matlab support is comprehensive. PMTK3 has been in maintenance mode for a few years, as the world has moved on Python in significant numbers. Nonetheless, PMTK3 should not be neglected for easy access to a wide variety of machine learning methods.

Install PMTK3:

git clone https://github.com/probml/pmtk3

cd pmtk3

From Matlab or Octave:

initPmtk3

which downloads supplementary files (one-time). Run programs like demos/bigO.m

Trim from time to end of video–discard beginning of video. In this examples, starting at 58 seconds.

ffmpeg -i in.mp4 -ss 00:00:58 -c copy out.avi

Trim from start to specified end time. In this example from 00:58 to 1:10.

ffmpeg -i in.mp4 -ss 00:00:58 -t 00:00:12 -c copy out.avi

Re-encode losslessly:

ffmpeg -i in.mp4 -ss 00:00:58 -t 00:00:12 -c:v ffv1 out.avi

Install POV-Ray by:

apt install povray

or build POV-Ray from source

Example POV-Ray tutorial

#include "colors.inc"
background { color Cyan }
camera {
    location <0, 2, -3>
    look_at  <0, 1,  2>
}
sphere {
    <0, 1, 2>, 2
    texture {
        pigment { color Yellow }
    }
}
light_source { <2, 4, -3> color White}

POV-Ray can accomplish photorealistic rendering via raycasting.

To pop up your default video player upon click in Beamer LaTeX-generated PDF, use the LaTeX syntax

\href{run:myvideo.avi}{cool video}

You must use either

• relative path (e.g. ../data/myvid.avi gfx/myvid.avi)
• fully resolved absolute path (e.g. /home/joe/data/myvid.avi)

These will NOT work

• ~
• $HOME

Matlab and GNU Octave can process PSPICE simulations using GNUCAP or NGspice.

Example for a voltage multiplier: RF energy harvesting PSPICE sim

A LaTeX Beamer presentation (slide deck) with a long table of contents as generated by

\tableofcontents

may run off screen.

Fix

add to LaTeX preamble (near top of main .tex file):

\usepackage{multicol}

Then the TOC slide will go over multiple columns. In this example Beamer slide, two column table of contents is specified:

\frame{
\begin{multicols}{2}
\tableofcontents
\end{multicols}
}

For Linux desktop environments programs show up in menus from:

• /usr/share/applications
• ~/.local/share/applications ← especially for WINE

Sometimes an application might not appear in the desktop menus because it doesn’t have a .desktop file in either of these locations. Try opening one of the .desktop files for a program that works, and saving as a new file, editing for a program you’d like to work the same way.

Reference