# Finding inverse of a matrix using Gauss – Jordan Method | Set 2

• Last Updated : 31 Jul, 2021

Given a Matrix, the task is to find the inverse of this Matrix using the Gauss-Jordan method.

What is matrix?

Matrix is an ordered rectangular array of numbers. Operations that can be performed on a matrix are: Addition, Subtraction, Multiplication or Transpose of matrix etc.

### Inverse of a matrix:

Given a square matrix A, which is non-singular (means the Determinant of A is nonzero); Then there exists a matrix which is called inverse of matrix A.

The inverse of a matrix is only possible when such properties hold:

1. The matrix must be a square matrix.
2. The matrix must be a non-singular matrix and,
3. There exist an Identity matrix I for which In general, the inverse of n X n matrix A can be found using this simple formula: where, Adj(A) denotes the adjoint of a matrix and, Det(A) is Determinant of matrix A.

### Methods for finding Inverse of Matrix:

Finding the inverse of a 2×2 matrix is a simple task, but for finding the inverse of larger matrix (like 3×3, 4×4, etc) is a tough task, So the following methods can be used:

1. Elementary Row Operation (Gauss-Jordan Method) (Efficient)
2. Minors, Cofactors and Ad-jugate Method (Inefficient)

### Elementary Row Operation (Gauss – Jordan Method):

Gauss-Jordan Method is a variant of Gaussian elimination in which row reduction operation is performed to find the inverse of a matrix.

Steps to find the inverse of a matrix using Gauss-Jordan method:
In order to find the inverse of the matrix following steps need to be followed:

1. Form the augmented matrix by the identity matrix.
2. Perform the row reduction operation on this augmented matrix to generate a row reduced echelon form of the matrix.
3. The following row operations are performed on augmented matrix when required:
• Interchange any two row.
• Multiply each element of row by a non-zero integer.
• Replace a row by the sum of itself and a constant multiple of another row of the matrix.

Example: • Augmented Matrix is formed as A:B • After applying the Gauss-Jordan elimination method: Below is the C++ program to find the inverse of a matrix using the Gauss-Jordan method:

## C++

 `// C++ program to find the inverse of Matrix.` `#include ``#include ``using` `namespace` `std;` `// Function to Print matrix.``void` `PrintMatrix(``float``** ar, ``int` `n, ``int` `m)``{``    ``for` `(``int` `i = 0; i < n; i++) {``        ``for` `(``int` `j = 0; j < m; j++) {``            ``cout << ar[i][j] << ``"  "``;``        ``}``        ``printf``(``"\n"``);``    ``}``    ``return``;``}` `// Function to Print inverse matrix``void` `PrintInverse(``float``** ar, ``int` `n, ``int` `m)``{``    ``for` `(``int` `i = 0; i < n; i++) {``        ``for` `(``int` `j = n; j < m; j++) {``            ``printf``(``"%.3f  "``, ar[i][j]);``        ``}``        ``printf``(``"\n"``);``    ``}``    ``return``;``}` `// Function to perform the inverse operation on the matrix.``void` `InverseOfMatrix(``float``** matrix, ``int` `order)``{``    ``// Matrix Declaration.` `    ``float` `temp;` `    ``// PrintMatrix function to print the element``    ``// of the matrix.``    ``printf``(``"=== Matrix ===\n"``);``    ``PrintMatrix(matrix, order, order);` `    ``// Create the augmented matrix``    ``// Add the identity matrix``    ``// of order at the end of original matrix.``    ``for` `(``int` `i = 0; i < order; i++) {` `        ``for` `(``int` `j = 0; j < 2 * order; j++) {` `            ``// Add '1' at the diagonal places of``            ``// the matrix to create a identity matrix``            ``if` `(j == (i + order))``                ``matrix[i][j] = 1;``        ``}``    ``}` `    ``// Interchange the row of matrix,``    ``// interchanging of row will start from the last row``    ``for` `(``int` `i = order - 1; i > 0; i--) {` `        ``// Swapping each and every element of the two rows``        ``// if (matrix[i - 1] < matrix[i])``        ``// for (int j = 0; j < 2 * order; j++) {``        ``//``        ``//        // Swapping of the row, if above``        ``//        // condition satisfied.``        ``// temp = matrix[i][j];``        ``// matrix[i][j] = matrix[i - 1][j];``        ``// matrix[i - 1][j] = temp;``        ``//    }` `        ``// Directly swapping the rows using pointers saves``        ``// time` `        ``if` `(matrix[i - 1] < matrix[i]) {``            ``float``* temp = matrix[i];``            ``matrix[i] = matrix[i - 1];``            ``matrix[i - 1] = temp;``        ``}``    ``}` `    ``// Print matrix after interchange operations.``    ``printf``(``"\n=== Augmented Matrix ===\n"``);``    ``PrintMatrix(matrix, order, order * 2);` `    ``// Replace a row by sum of itself and a``    ``// constant multiple of another row of the matrix``    ``for` `(``int` `i = 0; i < order; i++) {` `        ``for` `(``int` `j = 0; j < order; j++) {` `            ``if` `(j != i) {` `                ``temp = matrix[j][i] / matrix[i][i];``                ``for` `(``int` `k = 0; k < 2 * order; k++) {` `                    ``matrix[j][k] -= matrix[i][k] * temp;``                ``}``            ``}``        ``}``    ``}` `    ``// Multiply each row by a nonzero integer.``    ``// Divide row element by the diagonal element``    ``for` `(``int` `i = 0; i < order; i++) {` `        ``temp = matrix[i][i];``        ``for` `(``int` `j = 0; j < 2 * order; j++) {` `            ``matrix[i][j] = matrix[i][j] / temp;``        ``}``    ``}` `    ``// print the resultant Inverse matrix.``    ``printf``(``"\n=== Inverse Matrix ===\n"``);``    ``PrintInverse(matrix, order, 2 * order);` `    ``return``;``}` `// Driver code``int` `main()``{``    ``int` `order;` `    ``// Order of the matrix``    ``// The matrix must be a square a matrix``    ``order = 3;``    ``/*``float matrix = { { 5, 7, 9 },``                         ``{ 4, 3, 8 },``                         ``{ 7, 5, 6 },``                         ``{ 0 } };``*/``    ``float``** matrix = ``new` `float``*;``    ``for` `(``int` `i = 0; i < 20; i++)``        ``matrix[i] = ``new` `float``;` `    ``matrix = 5;``    ``matrix = 7;``    ``matrix = 9;``    ``matrix = 4;``    ``matrix = 3;``    ``matrix = 8;``    ``matrix = 7;``    ``matrix = 5;``    ``matrix = 6;` `    ``// Get the inverse of matrix``    ``InverseOfMatrix(matrix, order);` `    ``return` `0;``}`

Output:

```=== Matrix ===
5  7  9
4  3  8
7  5  6

=== Augmented Matrix ===
7  5  6  0  0  1
5  7  9  1  0  0
4  3  8  0  1  0

=== Inverse Matrix ===
-0.210  0.029  0.276
0.305  -0.314  -0.038
-0.010  0.229  -0.124```

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