Banded Gaussian elimination using python.

 you will be given A, b, and k. Your task will be to solve Ax=b via Gaussian elimination to take advantage of the banded structure so that your code doesn't perform any operations on the parts of the matrix that are zero (if you are stuck, see section 2.5.3 of Heath). No pivoting is required. The matrix is large enough that if you do not take advantage of the banded structure to make your code fast, your code will time out.