This 4 by 4 matrix will need elimination matrices E

_{21}and E_{32}and E_{43}. What are those matrices?A=[2, -1, 0, 0, -1, 2, -1, 0, 0, -1, 2, -1, 0, 0, -1, 2].

The first row is 2, -1, 0, 0.

The second row is -1, 2, -1, 0.

The third row is 0, -1, 2, -1.

The fourth row is 0, 0, -1, 2.

## Comments

Ayou gave me is multiplied on the left by the elimination matrix I came up with. That adds 1/2 times the first row ofAto the second row ofA, getting rid of that first -1.