Conveniently Specify General Banded Matrices
Mathematica 6 introduces a convenient symbolic representation for arbitrary banded matrices.
In[1]:=  |  MatrixPlot[
SparseArray[
Table[Band[RandomInteger[{1, 100}, 2], Automatic,
RandomChoice[{1, -1}, 2]] -> RandomReal[{-10, 10}], {100}], {100,
100}]] |
Out[1]=  |  |