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 |
  +----+-------+-------+-------+-------+