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— Function: grid:subgrid grid dimensions start &key destination drop

Create a grid from a block of an existing grid, e.g. a row from a matrix, or a block. The dimensions give the dimensions of the subgrid, and start gives the lowest values of each index which corresponds to the subgrid element with all index values zero. If drop is true, all singleton axes are dropped.

— Function: (setf grid:subgrid)

Set the subgrid of the grid. Specify the starting indices with start, and in the case that the subgrid has lower rank than the grid, which axes; default is the first (rank subgrid) axes.

The functions subgrid, (setf subgrid) select or set a region within a grid as a grid. For example, The 2 by 2 block starting at index 1,2 in the previous matrix is
     (subgrid (test-grid-double-float 'array '(3 4)) '(2 2) '(1 2))
     #2A((12.0d0 13.0d0) (22.0d0 23.0d0))