Stencil: Difference between revisions

{{Built-in|Stencil|⌺}} is a primitive [[dyadic operator]] that applies its left [[operand]] to (possibly overlapping) rectangular views of the right argument [[array]]. The [[shape]] and movement of the rectangular views are dictated by the right operand. It was introduced to [[Dyalog APL]] in version 16.0 and is also known as tessellation, moving window, [[wikipedia:stencil code|stencil code]] or cut. The operator can be used for computations involving the immediate neighbours of items in an array and has applications in image processing (particularly [[wikipedia:convolution (computer science)|convolution]]), artificial [[neural networks]] and, most famously, [[wikipedia:cellular automaton|cellular automata]]. The operator derives from a subset (specifically, case 3) of the functionality of [[J]]'s [[Cut]] operator (<syntaxhighlight lang=j inline>;.3</syntaxhighlight>),<ref>[[Eugene McDonnell]]: [https://www.jsoftware.com/papers/eem/life1.htm Life: Nasty, Brutish, and Short]. [[APL88]]. </ref> which in turn originates in the 3-cut mentioned in [[A Dictionary of APL]]<ref>[[Ken Iverson]]: [https://www.jsoftware.com/papers/APLDictionary.htm A Dictionary of APL]. [[APL Quote Quad]], Volume 18, Number 1, 1987-09.</ref>