The matrix e refers to identity matrix. In the multiplication of matrices, there is a matrix that plays a special role, such as 1 in the multiplication of numbers. This matrix is called identity matrix. It is a square matrix, and all the elements on the diagonal line (called the main diagonal line) from the upper left corner to the lower right corner are 1, and all the other elements are 0.

In mathematics, a matrix is a group of complex numbers or real numbers arranged in a rectangular array, which originated from a square matrix composed of coefficients and constants of equations. This concept was first put forward by British mathematician Kelly in19th century. Matrix is a common tool in applied mathematics such as advanced algebra and statistical analysis. The customized algorithm for specific matrix structures (such as sparse matrix and near-angle matrix) speeds up the operation speed in finite element method and other calculations.