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Thanks for great challenge, first of all (you were our taskmaster, right?) I didn't mention your solution, because it was kind of slow for comparisons. But now I see where it and challenge itself have originated. PDL is very TIMTOWTDI-ish, and range is ultimately important tool, to extract/address rectangular areas from ndarrays of any dimensions. But, eh-hm, don't you see that the POD you linked sings praises to wonders of broadcasting, which (i.e. broadcasting) you simply discarded? Broadcasting really only happens in this fragment:

...-> sumover-> sumover

which you replaced with

...-> clump(2)-> sumover

(Frankly, it's obvious I think that huge speed difference of Game-of-Life implementations in the linked tutorial is due to the way looping was generally performed rather than this "broadcasting" only, -- but perhaps that's how tutorials work.)

Consider:

sub sms_WxH_PDL_range ( $m, $w, $h ) { my ( $W, $H ) = $m-> dims; $m-> range( ndcoords( $W - $w + 1, $H - $h + 1 ), [ $w, $h ]) -> reorder( 2, 3, 0, 1 ) -> clump( 2 ) -> sumover } sub sms_WxH_PDL_range_b ( $m, $w, $h ) { my ( $W, $H ) = $m-> dims; $m-> range( ndcoords( $W - $w + 1, $H - $h + 1 ), [ $w, $h ]) -> reorder( 2, 3, 0, 1 ) -> sumover -> sumover } __END__ Time (s) vs. N (NxN submatrix, PDL: Double D [300,300] matrix) +-----------------------------------------------------------+ |+ + + + + + | 1.6 |-+ A +-| | | | | 1.4 |-+ +-| | | 1.2 |-+ +-| | A | | | 1 |-+ +-| | | | B | 0.8 |-+ +-| | A | | | 0.6 |-+ B +-| | | 0.4 |-+ A +-| | B | | A | 0.2 |-+ A B +-| | A B B | | A B B D D | 0 |-+ D D D D D D D D D C C +-| |+ + + + + + | +-----------------------------------------------------------+ 0 5 10 15 20 25 sms_WxH_PDL_range A sms_WxH_PDL_range_b B sms_WxH_PDL_lags C sms_WxH_PDL_naive D +----+-------+-------+-------+-------+ | N | A | B | C | D | +----+-------+-------+-------+-------+ | 2 | 0.015 | 0.008 | 0.000 | 0.000 | | 3 | 0.021 | 0.018 | 0.000 | 0.000 | | 4 | 0.044 | 0.021 | 0.000 | 0.000 | | 5 | 0.073 | 0.047 | 0.000 | 0.003 | | 6 | 0.101 | 0.060 | 0.000 | 0.000 | | 8 | 0.193 | 0.104 | 0.000 | 0.005 | | 10 | 0.294 | 0.138 | 0.000 | 0.005 | | 12 | 0.435 | 0.232 | 0.000 | 0.010 | | 16 | 0.711 | 0.344 | 0.000 | 0.015 | | 20 | 1.115 | 0.549 | 0.000 | 0.026 | | 25 | 1.573 | 0.828 | 0.000 | 0.047 | +----+-------+-------+-------+-------+

(I took liberty to use couple of numbers as args to ndcoords instead of matrix/slice, which only serves as source of these 2 numbers). Note, the matrix is now smaller than in previous tests. Both A and B versions are very much slower than the so far slowest "naive" variant. Though ndcoords builds a relatively large ndarray to feed to range, I think range is simply not written with speed/performance as its goal.

It's actually tempting to try to improve Game of Life PDL implementation from the tutorial:

use strict; use warnings; use experimental qw/ say postderef signatures /; use Time::HiRes 'time'; use PDL; use PDL::NiceSlice; use Test::PDL 'eq_pdl'; use constant STEPS => 100; my $x = zeroes( 200, 200 ); # Put in a simple glider. $x(1:3,1:3) .= pdl ( [1,1,1], [0,0,1], [0,1,0] ); my $backup = $x-> copy; printf "Game of Life!\nMatrix: %s, %d generations\n", $x-> info, STEPS; # Tutorial my $t = time; my $ct = 0; for ( 1 .. STEPS ) { my $t_ = time; # Calculate the number of neighbours per cell. my $n = $x->range(ndcoords($x)-1,3,"periodic")->reorder(2,3,0,1); $n = $n->sumover->sumover - $x; $ct += time - $t_; # Calculate the next generation. $x = ((($n == 2) + ($n == 3))* $x) + (($n==3) * !$x); } printf "Tutorial: %0.3f s (core time: %0.3f)\n", time - $t, $ct; # "Lags" my $m = $backup-> copy; $t = time; $ct = 0; for ( 1 .. STEPS ) { my $t_ = time; # Calculate the number of neighbours per cell. my $n = sms_GoL_lags( $m ) - $m; $ct += time - $t_; # Calculate the next generation. $m = ((($n == 2) + ($n == 3))* $m) + (($n == 3) * !$m); } printf "\"lags\": %0.3f s (core time: %0.3f)\n", time - $t, $ct; die unless eq_pdl( $x, $m ); sub _do_dimension_GoL ( $m ) { $m-> slice( -1 )-> glue( 0, $m, $m-> slice( 0 )) -> lags( 0, 1, ( $m-> dims )[0] ) -> sumover -> slice( '', '-1:0' ) -> xchg( 0, 1 ) } sub sms_GoL_lags ( $m ) { _do_dimension_GoL _do_dimension_GoL $m } __END__ Game of Life! Matrix: PDL: Double D [200,200], 100 generations Tutorial: 1.016 s (core time: 0.835) "lags": 0.283 s (core time: 0.108)

Sorry about crude profiling/tests; and improvement is somewhat far from what I expected. Even with "core time" singled out -- because next gen calculation is not very efficient (e.g. $n == 3 array is built twice), but that's another story -- which is "only" 8x better. Maybe all this glueing/appending to maintain constant matrix size and "wrap around" at edges takes its toll.


In reply to Re^2: Fast sliding submatrix sums with PDL (inspired by PWC 248 task 2) by Anonymous Monk
in thread Fast sliding submatrix sums with PDL (inspired by PWC 248 task 2) by Anonymous Monk

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