I know this answer already been posted but I am just looking for a little more detail.

A tridiagonal matrix is an nxn array in which has a[i][j] = = 0 if |i-j| > 1. What is the maximum number of non zero elements? How can they be stored in memory sequentially? Find a formula k= f(i,j) to store location a[i][j] in k, when |i-j| <=1 (you only want to store the nonzero elements). Do not write code. Code would work if you were manually converting the matrix from one form to the other all at once, but you need the formula to