Beginner needs help with basic function

The Assignment:

. Write a function called even_index that takes a matrix, M, as input argument and returns a matrix that contains only those elements of M that are in even rows and columns. In other words, it would return the elements of M at indices (2,2), (2,4), (2,6), ..., (4,2), (4,4), (4,6), ..., etc. Note that both the row and the column of an element must be even to be included in the output. The following would not be returned: (1,1), (2,1), (1,2) because either the row or the column or both are odd. As an example, if M were a 5-by-8 matrix, then the output must be 2-by-4 because the function omits rows 1, 3 and 5 of M and it also omits columns 1, 3, 5, and 7 of M.

My Function:

function even_index(M)
    M(2:2:end,2:2:end)

The Problem?

If I go to command window and do M = [1 2 3;4 5 6] and create a matrix, and then run "even_index(M)" I get the correct answer (5). However, when i use the required "grader " program, It says

Problem 2 (even_index):
                                       Testing with argument(s) [1 2 3;4 5 6]
    Feedback: Your program made an error for argument(s) [1 2 3;4 5 6]

      Your solution is _not_ correct

What am I missing?

[Sarah Heady]

Hey Charlie did you ever figure this out? I have this code: function M_out = even_index(M) M_out = M(2:2:end, 2:2:end); end -- but it always gives me this error: Not enough input arguments. --What did you do to fix this error?

[Sarah Heady]

Never mind. I was running the wrong thing.

Answer 1

[Walter Roberson]

Your function does not return anything, it displays the results instead. Functions that return something have an "=" on the function line.

[Charlie Harris]

Thank You, I wondered about that? I will keep trying.