Stencil: Difference between revisions

For a call <source lang=apl inline>f⌺s</source> the right operand <source lang=apl inline>s</source> can in general be a two-row [[matrix]] of strictly positive integers, where the first row describes the dimensions of the rectangles that will be passed to <source lang=apl inline>f</source> and the second row describes the movement along the different [[axis|axes]]. When using stencil <source lang=apl inline>(f⌺s)Y</source> the right operand <source lang=apl inline>s</source> in general has <source lang=apl inline>≢⍴Y</source> columns. If it has fewer, the rectangles are cut out of the [[major cell]]s of the <source lang=apl inline>(≢⍴Y) - ≢1⌷s</source> axis of <source lang=apl inline>Y</source>. If <source lang=apl inline>s</source> is a vector or scalar it describes only the size of the rectangles and the movement defaults to 1. Rectangles are centred on [[element]]s of <source lang=apl inline>Y</source> whose [[index|indices]] differ by the movements in <source lang=apl inline>s</source> (defaulting to 1), starting with the first element in [[ravel order]]. For a matrix, this is the top left. For even window sizes, the centring is instead on the space between elements or [[cell]]s. Along the edges of the [[argument]] array, the windows are thus subject to be padded with [[fill element]]s. The number of fill elements in along each axis is given as a vector left argument on each call of <source lang=apl inline>f</source> for the respective [[subarray]].