For large submatrices one can use a Fourier transforms to perform the convolution, as in

use v5.36;
use PDL;
use PDL::FFT;
my $matrix=pdl(shift); # Format "[[m11,m21...],[m21...]...]"
my $width=my $w=shift;
my $height=my $h=shift;
my $small=ones($w%2?$w:$w+1, $h%2?$h:$h+1);
$small->slice(-1).=0, ++$w unless $w%2; # zero row and/or column for e
+ven kernels
$small->slice([],-1).=0, ++$h unless $h%2;
my $kernel=kernctr($matrix, $small); #full kernel
my $result=$matrix->copy;
$result->fftconvolve($kernel);
say "$matrix $width $height -> ",
    $result->slice([floor(($width-1)/2),floor(-($width+1)/2)],
                   [floor(($height-1)/2),floor(-($height+1)/2)]);

[download]

It would be interesting to also compare it.

In reply to Re^3: Fast sliding submatrix sums with PDL (inspired by PWC 248 task 2) by wlmb
in thread Fast sliding submatrix sums with PDL (inspired by PWC 248 task 2) by Anonymous Monk

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