Problem 4: Make a 20 by 20 matrix in which diagonal elements are 21, 22, 23, 24 ... 40 and elements below the diagnol are a ¡¡ = 2(i²¯j²) and elements above the diagnol are 4×(i+j) ij Note: You must use if, elseif, else, end or/and if, end or/and if, else, end commands in MATLAB.