Thanks @Adám and @rabbitgrowth for the examples of the rank operator. Starting to understand it. @xpqz also described it quite clearly in the transcripts. I think rank and power are the most difficult operators.

But at the same time maybe also the most powerful

@Richard well there you have it. You’re ready for dyadic transpose next for your array programming black belt.

In this example about stencil why does the padding start at 1 to -1 instead of all zeros? The Left Argument i

I think I get it. The number indicate what rows or columns are missing from the 3 3 matrix.

The left argument indicates the size of the overlap in each axis for that block. The sign indicates the direction.

A block with 0 0 has no extra rows or columns. A block with 0 1 has no extra rows, but an extra column to the left. 0 -1 means an extra column to the right, etc.

I talked a bit about this in my APL Seeds'22 talk (dyalog.tv/APLSeeds22/?v=h-kUZfdPbdU) about 10 mins in.

Thanks! I will take a look.

That was quite helpful. I am enjoying working my way through your book and slowly beginning to understand things. I appreciate it.

Good to hear -- I'm always interested in hearing what people using it think. I see it as a bit of a work in progress and keep adding to it occasionally.

I spoke about how it came to be at Dyalog '21, too: dyalog.tv/Dyalog21/?v=qrWCYPFfsCU

It pairs well with the APL cultivations you collected. I've been using that as a supplement. You might collect some additional learning resources in the introduction. Overall I would say it is the best introductory APL text I've come across so far. I say that as someone who has slogged through the first 160 pages of Mastering APL before moving on to your book.

Sorry to be clear. I know there is a section in the intro about other resources. I just find this APL Collections to be more helpful than this collection of bookmarks

Thanks again.

I wanted to start each chapter with a bunch of references to other material, partly for my own use. There is also a comprehensive list on APLWiki: aplwiki.com/wiki/Learning_resources

That is fantastic bookmarked!

It's a community effort; if you find that something is missing, do add it to that list.

Another recent APL resource is the Array programming topic on the fast.ai forum, if you haven't found it: forums.fast.ai/c/array-programming/56