Question 4 (20 points) The trace of a square matrix is the algebraic sum of all the elements along the diagonal from top left to bottom right. In MATLAB, there exists a pre-defined function trace that achieves so. Write a function m-file named mytrace that calculates and returns the trace of a square matrix. It returns an empty vector if the input matrix is not square. Type the following in your script m file as test data mytrace ([1 2 3; 4 5 6; 7 8 9]) mytrace([1 2])