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I think dummy dimensions add only a few bytes to PDL-struct header, but your approach really physicalizes arrays from 2D to 4D (edit: well, it's still same 2D but squared dimensions for this example, sorry), which has grave consequences for performance. If no-one ever needs Kronecker product of 80x80 matrices, then count this comment as another nitpick :). + Note report of memory consumption assumes Win32, so disable/replace otherwise.

use strict; use warnings; use feature 'say'; use PDL; use Time::HiRes 'time'; use constant DIM => 80; my $x = random DIM, DIM; my $y = random DIM, DIM; report( 'choroba, vr', \&kronecker_product, $x, $y ); report( 'etj', \&kron, $x, $y ); sub report { my ( $monk, $code, $x, $y ) = @_; my $t = time; my $k = $code-> ( $x, $y ); say "$monk:"; say 'time: ', time - $t; say 'memory: ', mem(); } sub mem { qx{ typeperf "\\Process(perl)\\Working Set Peak" -sc 1 } =~ /(\d+)\.\d+\"$/m; ( my $s = $1 ) =~ s/(\d{1,3}?)(?=(\d{3})+$)/$1,/g; return $s } sub kronecker_product { use PDL::NiceSlice; my ( $x, $y ) = @_; ( $x( *1, *1 ) * $y ) -> clump( 0, 2 ) -> clump( 1, 2 ) } sub PDL::dupN { my ($this, @times) = @_; return $this->copy if !grep $_ != 1, @times; my $sl = join ',', map ":,*$_", @times; $this = $this->slice($sl); $this = $this->clump($_, $_+1) for 0..$#times; $this; } sub PDL::inflateN { my ($this, @times) = @_; return $this->copy if !grep $_ != 1, @times; my $sl = join ',', map "*$_,:", @times; $this = $this->slice($sl); $this = $this->clump($_, $_+1) for 0..$#times; $this; } sub kron { my ($x,$y) = @_; $x->inflateN($y->dims) * $y->dupN($x->dims +) } __END__ choroba, vr: time: 0.0958220958709717 memory: 355,741,696 etj: time: 8.45677018165588 memory: 2,977,234,944

Edit 2. By the way, while we are at this example, the PDL::NiceSlice says

  • arguments should not be quoted
  • lone '*' inserts a dummy dimension of order 1

but I see that lone unquoted star(s) cause Perl to produce a warning:

Use of uninitialized value in concatenation (.) or string

so I had to insert a pair of very unsightly "1"'s, which of course devalues code nicety by half at least:). Is this a bug in PDL::NiceSlice, documentation flaw, or just me reading it incorrectly?


In reply to Re^3: Kronecker Product by vr
in thread Kronecker Product by choroba

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