A simple example of finding the inverse matrix of a 4x4 matrix, using Gauss-Jordan elimination

Last updated: Jan. 3, 2019
  Find the inverse matrix of a 4x4 matrix, , using Gauss-Jordan elimination. .

Explanation

  To obtain the inverse matrix, we define a matrix in which the matrix $A$ and the unit matrix $I$ are arranged side by side, . This matrix is called augmented matrix. We transform the matrix $A$ in the augumented matrix to the unit matrix $I$ by performing elementary row operations, i.e., . As a result, the unit matrix in the right half of the augmented matrix becomes the inverse of $A$. This method of finding the inverse matrix is called Gauss-Jordan elimination. (Here, the dotted line drawn vertically is merely a convenience for distinguishing between the left side and the right side.)
  According to this method, we perform elementary row operations as follows.   Therefore, we obtain