sub sms_WxH_PDL_lags ( $m, $w, $h ) {
    my ( $W, $H ) = $m-> dims;
    
    return $m
        -> lags( 0, 1, 1 + $W - $w )
        -> sumover
        -> lags( 1, 1, 1 + $H - $h )
        -> xchg( 0, 1 )
        -> sumover
        -> slice( '-1:0,-1:0' )
}

$m = 1 + sequence 4, 3;
print $m,
    sms_WxH_PDL_lags( $m, 2, 2 ),
    sms_WxH_PDL_lags( $m, 3, 3 ),
    sms_WxH_PDL_lags( $m, 4, 3 ),
    sms_WxH_PDL_lags( $m, 1, 1 );

__END__

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