Efficient Conjugate Gradient Method for Symmetric Banded Matrix

Given symmetric banded matrix A,this code efficiently uses conjugate gradient method to solve Ax=b.

This code uses conjugate gradient method to solve the linear system
Ax= b, where A is symmetric and banded. A is first stored in a
compactstorage mode, using the function "compactstorage", and then
conjugate gradient method is applied to the compactly stored matrix.
Input: A, initial guess x, vector b, tolerance called epsilon and
maximum number of iteration called MaxIter.
Output: computed solution x and number of iteration called Iteration.