MEAN   Average or mean value.
    For vectors, MEAN(X) is the mean value of the elements in X. For
    matrices, MEAN(X) is a row vector containing the mean value of
    each column.  For N-D arrays, MEAN(X) is the mean value of the
    elements along the first non-singleton dimension of X.
 
    MEAN(X,DIM) takes the mean along the dimension DIM of X. 
 
    Example: If X = [0 1 2
                     3 4 5]
 
    then mean(X,1) is [1.5 2.5 3.5] and mean(X,2) is [1
                                                      4]
 
    See also MEDIAN, STD, MIN, MAX, COV.