The second example starts by declaring a 3-by-3 matrix m which is initialized using the Random() method with random values between -1 and 1. The next line applies a linear mapping such that the values are between 10 and 110. The function call MatrixXd::Constant(3,3,1.2) returns a 3-by-3 matrix expression having all coefficients equal to 1.2. The rest is standard arithmetic.