(a) The vector x R N has L different entries. For example, L = 4 for x = [ 3 , 4 , 4 , 5 , 3 , 1 , 5 , 3 ] . One can express x as x = S u , where u R L satisfies ( u ) i < ( u ) j if i < j and S is a matrix that contains only zeros and ones. Write the function repeated_entries, which takes x as input and returns S and u . .