## Multi-pendulum Harmonograph simulator using numpy and matplotlib

22nd June 2017

This is a simple harmonograph simulator to generate random-ish harmonographs. It asks for the number of pendulums, and exits if the number is 0. It also asks for the frequency spread, which means roughly, how far from integer may the frequencies go. The nearer to integer they are, the ‘cleaner’ looking the harmonographs are, but […]

## A Neural Network in Python, Part 2: activation functions, bias, SGD, etc.

9th February 2017

This is Part 2 of A Neural Network in Python, which was a very simple neural network to learn the XOR function. This part builds on that example to demonstrate more activation functions, learning a simple math function, adding a bias, improvements to the initial random weights, stochastic gradient descent, mean square error loss function, […]

## A Neural Network in Python, Part 1: sigmoid function, gradient descent & backpropagation

31st January 2017

In this article, I’ll show you a toy example to learn the XOR logical function. My objective is to make it as easy as possible for you to to see how the basic ideas work, and to provide a basis from which you can experiment further. In real applications, you would not write these programs from scratch […]

## Have we already seen this number? (deja vu again)

8th April 2016

I had a phone interview for a Python job the other day. It started out really well, he was very impressed with my CV and called me a ‘rocket scientist’. But then we got down to the technical questions and my brain decided to go out to lunch, and (yet again) I managed to snatch defeat […]

## Hello World 2, in Python 3

24th March 2016

Hello World is the famous minimal introductory program for many programming languages. But as soon as it’s served its purpose, it’s discarded in the dust of history for more exciting things, such as data types or expressions… This is politically incorrect discrimination and must be stopped! This loyal and true didactic program should have the right to […]

## Spectral Harmonographs

5th October 2015

This Python + Pygame program draws the trace of 4 decaying sine waves, 2 per axis, with rainbow colours. It generates a sequence of random harmonographs. A harmonograph is a mechanical device typically seen in science museums, that has two or more pendulae with attached pens, that can draw on a sheet of paper. The pendulae are […]

## Number guessing game

1st October 2015

The number guessing game incorporates several simple but important elements of elementary programming and is a good candidate for an introductory programming example. If you’ve seen any programming course, you’ve probably seen the “Hello World” program. In Python it’s: print (“Hello World”)This is done to get the student(s) quickly to the point of having successfully installed […]

## A Graphical Dice Simulator

31st May 2015

This PyGame program simulates the roll of a die (or dice if you prefer). It’s a fairly simple, straightforward thing to do, though it may be worth noting that the spots display is oh-so-slightly clever. Some spots appear in more than one number, e.g. the middle spot is in all the odd numbers, hence the […]

## Extensible Harmonograph

18th May 2015

Often seen in science museums, the harmonograph is a device that combines wave motions (e.g. from some pendulums) to move a pen resting on a sheet of paper. These movements result in attractive patterns. This device can be simulated easily in a computer program such as the following one. The principle is that the wavy […]

## Binary Search

27th April 2015

Binary Search is one of the most fundamental computer algorithms. Given an ordered list of some data (names, numbers, …) find out if it contains a particular item. For example, consider the list: 2, 4, 5, 7, 8, 11, 12. If we ask if it contains the number 5, the algorithm should return 2 (counting […]

## Random Walk

18th April 2015

A colourful random walk. The basic idea is very simple: choose a random heading in the range 0:360 degrees. Step in that direction. Choose another random heading & step again. Do this 2,000 times. As a bonus, we go through all the colours of the rainbow (or something similar) from beginning to end. Dealing with […]