MATLAB: I would like to select the values from the 2nd column which have the less than 5 value in the 1st column. So the matrix looks maybe like this:

Question

1.  column:  [ 3 5 8 2 6 4 10 6 1 9 2 6 ]  
2.  column:  [ 11 32 24  47 15 33 39 3 43 8 55 15 ]

Answer 1

Use logical indexing:

>> M = [ 3 5 8 2 6 4 10 6 1 9 2 6; 11 32 24  47 15 33 39 3 43 8 55 15 ].';
>> M(M(:,1)<5,:)
ans =
    3   11
    2   47
    4   33
    1   43
    2   55

Basic MATLAB usage like this is covered in the introductory tutorials:

http://www.mathworks.com/help/matlab/getting-started-with-matlab.html