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Showing posts from May, 2013

Winner of the minimum coin problem

I posted a puzzle about coins and change and promised a prize (a copy of The Geek Atlas) to one of the solutions picked by me. The following people provided solutions:

1. Matt

2. Michael Bauer

3. Asger Drewsen

4. vext01

5. Dubya

6. Josh

7. Anatoli Plotnikov

8. Matt Hickford

As that's a convenient 8 people I've chosen a winner by the roll of a d8.


 So the winner is #7, Anatoli Plotnikov.

The Four Power Days

Today, May 5 is written 5/12 in the US and 512 is a power of 2, it's \(2^9\). I tweeted that and received a rapid reply from Peter Inglesby that in UK-style dates it's 12/5 which is 125 which is \(5^3\). Which made me wonder whether there were other dates that had the same property in the US and UK on the same day.

Peter wrote a quick script:
and determined that there are four such dates:

March 24: US 3/24; \(324 = 18^2\). UK 24/3; \(243 = 3^5\)

May 12: US 5/12; \(512 = 2^9\). UK 12/5; \(125 = 5^3\)

June 25: US 6/25; \(625 = 5^4\). UK 25/6; \(256 = 2^8\)

December 5: US 12/5; \(125 = 5^3\). UK 5/12. \(512 = 2^9\)

Now I just need to think up a mystical significance to this, start a religion and retire on the proceeds.

A home made periodic table

One of my slow burn projects has been to make and display a periodic table of elements using element samples that I have been able to find or make myself. This is what it currently looks like:


The poster itself is actually a blown up version of the poster that comes with the quirky book Wonderful Life with the Elements: The Periodic Table Personified by Bunpei Yorifuji. Each element is represented by a person (or robot) and characteristics of the person reflect the element itself (such as its state at 'room temperature', its radioactivity, and when it was discovered).

Having got the poster enlarged I had a custom frame made using the cheapest online source I could find. To store each element I'm using 1/2 dram clear glass vials with black polypropylene caps that are lined with polyvinyl. This vial are very small (they are pictured here with my international object sizing tool) so that the overall periodic table is not too large.


It is possible to buy samples of the elemen…

The two problems I had to solve in my Oxford interview

Back in the 1980s I went to Oxford University and studied Mathematics and Computation (this was almost the entire Mathematics course plus Computer Science added on; the degrees offered today are a little different).  Having sat the mathematics entrance exam and gone through all the mathematics interviews I had interviews in the Programming Research Group (now the Department of Computer Science). During those interviews two specific programming/algorithm design questions were posed. Here they are (I made up names for them).

The Z Machine

A computer is constructed with a simple memory layout. It has an unlimited amount of memory and each memory location is numbered so that a program can refer to it. Each memory location can store a single number or be uninitialized. In the following diagram memory locations that are blank are uninitialized some other memory locations have numbers in them.


The computer's CPU only has three instructions Z, I and J as follows:

Z. This instruction zeroes…

From the ground up (or how to encourage a school boy)

Following on from my popular blog post about coding by hand in 1985 I dug into my pile of old stuff to look at how myself and another boy at school reverse engineered the Research Machines CHAIN network and built everything from networking protocols to a network management system in assembly language.

In 1982 Research Machines in the UK launched the LINK 480Z Z80 based machine that had an optional 800kbps proprietary network called CHAIN. My upper school got a small network of them linked to a file server running MP/M. The 480Z's would boot from the file server across the network.


Unfortunately, the entire network protocol was undocumented by Research Machines and unpublished. Myself and another boy, P, decided to reverse engineer because we wanted boot control and we wanted network access. Disassembling the running operating system (often using its front panel, which was on screen and not via flashing lights) we were able to determine that the Z80RST 8 instruction was used to se…