Diagonal matrix - All entries not on the main diagonal (the diagonal from the upper left to the lower right corner) are zero. Especially easy to raise to a power.
... Pencil Museum[?], Keswick
Dock Museum[?], Barrow-in-Furness[?]
Kendal Museum[?]
Museum of Lakeland Life[?], Kendal[?]
Tullie House Museum, Carlisle
Derby and ...