./backlog: Charlie's blog

meanderings through tidbits of mathsy computery stuff

Fixing the UX of IP Addresses

Remembering IP addresses has long been a pain point for system administrators. They’re long, clunky and difficult to remember - essentially a 12-digit phone number for internet-connected machines. Trying to remember the IPs of the endless reams of servers that you manage (was it x.x.x.y? or was it y.y.y.z?) is difficult - after all, that’s why we have DNS. Trying to remember or communicate all 12 digits (which can be up to 20 syllables long!

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Making a Mosaic from Random Images

You may have noticed that this blog has been quiet for a while. That’s because I’ve been writing my undergraduate dissertation (the subject of another soon-to-be blog post, and hopefully a published paper)! This post is to make up for my lack of activity on here lately – so let’s get started. If you’ve seen any recent pop art (or in fact, kept abreast of the arts section in most newspapers), you’ll probably have seen things like this (found here);

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Manually Calculating an SVM's Weight Vector

Note: This post assumes a level of familiarity with basic machine learning and support vector machine concepts. Let’s say that we have two sets of points, each corresponding to a different class. Let’s call these classes positive and negative (but really they could be any binary class - pink, or not pink, cucumber or not cucumber, and so on). For simplicity, I’m assuming two dimensions, but really the only requirement is that your data is separable by a hyperplane.

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Online Backup of Ghost Blog

I’ve been running a Ghost blog and some other pieces of software on my server for the last couple of years, and to my shame, until recently I hadn’t sorted out a proper backup scheme. Being paranoid, I set up Tarsnap to perform daily backups of my Git repositories and home directory, and weekly backups of my Ghost blog, GitLab, and other stuff. Annoyingly, to back up the database for my Ghost blog, I kept having to issue service ghost stop - that is, I had to stop my blog serving temporarily while I backed up the database.

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Yubikey not working on Linux? It's probably udev

I recently bought a GitHub-branded U2F Yubikey and was waiting desperately for it to arrive in the post. Unfortunately, when it came, I couldn’t get it working on my Linux machine for love nor money. I spent a couple of hours Googling around and finally found the solution - it was actually on Yubico’s website all along, but not very well publicised. You need to add some udev rules - I’ll copy the instructions and rules below so that I can refer back to them in the future :-).

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