The BandMatrix(L) command constructs a band Matrix from the data provided by L.

Each list element in L is used to initialize a diagonal. The st element of L is placed along the main diagonal. The other diagonals are placed in relation to it:  is placed in the jth subdiagonal for  and  is placed in the kth superdiagonal for . If any list element is shorter than the length of the diagonal where it is placed, the remaining entries are filled with 0.

If n is omitted  in the calling sequence, BandMatrix attempts to place an equal number of sub- and super-diagonals into the resulting Matrix by using  subdiagonals.