Parenthesis vs brackets for matrices When I first learned linear algebra, both the professor and the book used brackets like `[` and `]` to enclose matrices. However, in my current differential equations textbook, matrices are enclosed by parenthesis, and I suddenly realize everybody else are using them too. So are brackets/parenthesis for enclosing matrices always totally interchangeable?

It is just a question of notation and what you are comfortable with. The only thing you might want to be aware is |A| stands for determinant of the matrix A and hence cannot be used in place of () or [] to represent the matrix