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Algorithms

Towards Improvements to Stencil

Background The stencil operator ⌺ was introduced in Dyalog version 16.0 in 2017. Recently we received some feedback (OK, complaints) that (a) stencil does… Read

June 2020

Roger Hui

Ascending and Descending

Lexicographic Ordering Lexicographic ordering is what the APL primitives ⍋ and ⍒ provide: ⎕io←0 ⍝ ⎕io delenda est ⎕rl←7*5 ⍝ to get… Read

February 2019

Roger Hui

Krypto

In the 2016 Year Game, the task was to generate the numbers 0 to 100 using APL primitives and the digits 2 0 1 6 in that order. For example, 20=16 ×2016… Read

May 2017

Roger Hui

Beauty and the Beast

Finally, the last accessory I ordered for my Raspberry Pi Zero (that’s the little red thing behind my keyboard) has arrived – an Acer 43″… Read

March 2017

Morten Kromberg

Charting Reaction Times on the Raspberry Pi

Earlier this week I collected some reaction timer data on my Pi using the BBC micro:bit as an input device. I only produced an “ASCII art” chart at… Read

March 2017

Morten Kromberg

APL Exercises

These exercises are designed to introduce APL to a high school senior adept in mathematics. The entire set of APL Exercises has the following sections:… Read

September 2016

Roger Hui

50847534

⎕io←0 throughout. I was re-reading A Mathematician’s Apology before recommending it to Suki Tekverk, our summer intern, and came across a statement… Read

September 2016

Roger Hui

Shuffle Faster Please!

Andy reported that in the shuffle QA some functions take a long time: m9249 “4½ days so far” rankop 21.5 hours… Read

May 2016

Roger Hui

The Halting Problem Rendered in APL

The halting problem is the problem of determining, from a description of a program and an input, whether the program will finish running or continue to run… Read

April 2016

Roger Hui

Quicksort in APL Revisited

A message in the Forum inquired on sorting strings in APL with a custom comparison function. First, sorting strings without a custom comparison function… Read

February 2016

Roger Hui

Permutations

I started composing a set of APL exercises in response to a query from a new APL enthusiast who attended Morten’s presentation at Functional Conf,… Read

July 2015

Roger Hui

In Praise of Magic Functions: Part II

Part I of this post was concerned with the development speed and execution speed of magic functions and should be read before this post. Benefitting from… Read

June 2015

Roger Hui

In Praise of Magic Functions: Part I

A magic function is an APL-coded (dfn) computation in the C source of the interpreter. For example, some cases of ∧.= are coded as… Read

June 2015

Roger Hui

Changes of Heart

Karen Shaw started the ball rolling (hearts afluttering?) by asking Jay Foad to come up with a one-liner for St. Valentine’s Day; he then solicited… Read

February 2015

Roger Hui

Solving the 2014 APL Problem Solving Competition – Cryptography Problem 3

This post is the continuation of the series where we examine some of the problems selected for the 2014 APL Problem Solving Competition. In this post… Read

February 2015

Jay Foad

Solving the 2014 APL Problem Solving Competition – Cryptography Problem 2

This post is the continuation of the series where we examine some of the problems selected for the 2014 APL Problem Solving Competition. In this post… Read

January 2015

Jay Foad

Solving the 2014 APL Problem Solving Competition – Cryptography Problem 1

This post is a continuation of the series where we examine some of the problems selected for the 2014 APL Problem Solving Competition. I’ll start by… Read

January 2015

Jay Foad

The Diamond Kata

Acknowledgments Morten Kromberg is the other co-author of this text but the blogging software prevents his being listed as such. We are indebted to Jay Foad,… Read

January 2015

Roger Hui

Three-and-a-bit

The most obvious expression for computing π in APL is ○1. But what if you can’t remember how ○ works, or your O key is broken, or you feel like… Read

January 2015

Jay Foad

Solving the 2014 APL Problem Solving Competition – it’s as easy as 1 1 2 3…

The winners of the 2014 APL Problem Solving Competition were recognized at the Dyalog ’14 user meeting and had a chance to share their… Read

November 2014

Brian Becker

Why Dyalog ’14 was a Shear Delight

Recent versions of Microsoft Windows support touch screens, which of course means that applications can respond to events originating from touches. Microsoft… Read

October 2014

John Daintree

Turning to a Heading with an MPU-9150

As the odour of fried electronics dissipates in the air, I’m unexpectedly afforded the opportunity to write this blog post a day or two earlier than… Read

September 2014

Morten Kromberg

Dancing with the Bots

Last week the ‘bots were busy preparing for the J Language Conference in Toronto, where they made their first public appearance together. Upon returning… Read

August 2014

Morten Kromberg

Aligning Diff Output

‘Bots are off limits this week so here is a story from this year’s Iverson College – a fantastic week spent in the company of a wonderful mixture of… Read

July 2014

Morten Kromberg