Re: first stumbling steps in PDL

TIMTOWTDI, but PDL is not about explicit loops. Not how it works. Consider this vector:

pdl> p $v = pdl split '', '30373'
[3 0 3 7 3]
[download]

Now then e.g. the cumulative sum or running total:

pdl> p cumusumover $v
[3 3 6 13 16]
[download]

Not very useful, but I have a vague feeling that "cumulative maximum" would be handy if someone is looking at a forest. You could type

pdl> ?? cumulative
[download]

to investigate what's available. OK, then, consider "strictly lower triangular matrix" or whatever it's called in mathematics if non-zero members are all 1's:

pdl> p $SLTM

[
 [0 0 0 0 0]
 [1 0 0 0 0]
 [1 1 0 0 0]
 [1 1 1 0 0]
 [1 1 1 1 0]
]
[download]

Hm-m, looks interesting. Not sure about forestry, but what if it's multiplied by our vector?

pdl> p $SLTM * $v

[
 [0 0 0 0 0]
 [3 0 0 0 0]
 [3 0 0 0 0]
 [3 0 3 0 0]
 [3 0 3 7 0]
]
[download]

That's even more interesting! What could we use this result for? What about computing maximum over rows?

pdl> p maxover $SLTM * $v
[0 3 3 3 7]
[download]

Now that's what I call interesting! Isn't it cumulative maximum of all elements before current for original vector? Let's check it without further ado:

pdl> p $v > maxover $SLTM * $v
[1 0 0 1 0]
[download]

But wait, that's exactly the answer we were looking for -- what trees are seen if forest patch is looked at from the left!

And all the rest was just further expansion of investigation performed above.

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Re^2: first stumbling steps in PDL by etj (Priest) on Feb 02, 2024 at 19:12 UTC
A slightly more concise way to get a lower triangular matrix of 1s: `use PDL::LinearAlgebra; sub ltm { my ($size, $strictly) = @_; my $ltm = ones($size,$size)->tricpy(1); $strictly ? $ltm - identity($size) : $ltm; }` [download]	[reply] [d/l]
Re^3: first stumbling steps in PDL by jo37 (Curate) on Feb 02, 2024 at 20:54 UTC
Is there an advantage of using `tricpy` over `mtri`? At least `mtri` may be called without argument when an upper triangle is requested, while with `tricpy` it is always required. Greetings, -jo `$gryYup$d0ylprbpriprrYpkJl2xyl~rzg??P~5lp2hyl0p$`	[reply] [d/l] [select]
Re^4: first stumbling steps in PDL by etj (Priest) on Feb 03, 2024 at 03:54 UTC
I'd say use whatever you find works! `tricpy` should clearly allow a default value of 0. Feel like making a PR? You'd have to make a `PMCode` function :-)	[reply] [d/l] [select]
Re^5: first stumbling steps in PDL by jo37 (Curate) on Feb 08, 2024 at 14:17 UTC
Re^6: first stumbling steps in PDL by eyepopslikeamosquito (Archbishop) on Feb 08, 2024 at 21:37 UTC
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Re^6: first stumbling steps in PDL by etj (Priest) on Feb 20, 2024 at 11:31 UTC
Re^6: first stumbling steps in PDL by etj (Priest) on Feb 11, 2024 at 00:16 UTC
Re^5: first stumbling steps in PDL by jo37 (Curate) on Feb 05, 2024 at 20:18 UTC
Re^6: first stumbling steps in PDL by etj (Priest) on Feb 06, 2024 at 17:58 UTC
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Re^5: first stumbling steps in PDL by jo37 (Curate) on Feb 04, 2024 at 09:56 UTC
Re^3: first stumbling steps in PDL by etj (Priest) on Feb 04, 2024 at 23:07 UTC
Today it was bugging me that there is no `tritosquare`, to provide another way to make a lower-triangular matrix. Now there is, on git `master` and soonish to be released: `pdl> p ones(10)->tritosquare [ [1 0 0 0] [1 1 0 0] [1 1 1 0] [1 1 1 1] ]` [download]	[reply] [d/l] [select]
Re^3: first stumbling steps in PDL by jo37 (Curate) on Feb 06, 2024 at 08:30 UTC
A slightly different approach for a strictly lower triangular matrix: `use PDL::LinearAlgebra::Real ... tricpy(zeros($size,$size), 0, my $sltm = ones($size, $size));` [download] Greetings, -jo `$gryYup$d0ylprbpriprrYpkJl2xyl~rzg??P~5lp2hyl0p$`	[reply] [d/l]
Re^4: first stumbling steps in PDL by etj (Priest) on Feb 06, 2024 at 16:45 UTC
Beautiful, with fewer operations!	[reply]