When using a matrix as input, all conditions are not met? Why?

function gradesFinal = computeFinalGrades(grades)
%computeFinalGrades calculates the final grade 
%
%Input  grades: a NxM matrix, where N is the number of students and M is 
%       number of assigments
%Output gradesFinal: a vector with length N, which contains the final grade
%       for each of N students

%Calculation of the final grade, rules:
%   1. only one assignment (M=1): the final grade is the grade that has 
%      been given for that assigment
%   2. if there are two or more assigments (M>1): lowest grade is not
%      included. Final grade is the mean of M - 1 highest grades, rounded
%      to nearest grade on scale, using function: roundGrade
%   3. if -3 has been given, no matter how many assigments the final grade
%      is -3.

%Find the dimension of the input grades
[N M] = size(grades);

i = 1:M;
% The logical vector to include the data:
includedData = true(size(grades, 1), 1);

% The three ways to calculate the final grade:
if M == 1
    includedData = grades(i,M);
    gradesFinal = roundGrade(includedData);
elseif any(grades == -3)
    gradesFinal = -3;
elseif M > 1
    includedData = (sum(grades')-min(grades'))/(M-1);
    gradesFinal = roundGrade(includedData);
end
end

The function works fine when i am using a vector as input, then it comes out with the final grade and the conditions also works. But when i use a matrix (what the input actually should be), it won't come out as -3 if N has -3 in it... What do this code lack?

Ex. computeFinalGrades([-3 3 7 5 4.5]) --> out: -3 With matrix: mat =

    2.0000    3.0000    4.0000   -3.0000
    5.0000    0.6000    2.0000    5.5000
    2.0000    5.0000    9.0000    8.0000

Output: ans =

     4     4     7
But actually it should be: -3 4 7

"roundGrade" is another function that l made