how to write a loop to read two columns for a matrix each time

Hi fellows, I have a matrix called tt (50*40) and I need to read two columns from it each time. And this is my code

if true
  %  for i=1:20
  subdata=tt(:,2i-1:2i);
    end

end

but in this way I get the error message is "Subscript indices must either be real positive integers or logicals." Any one know how to solve it? Or do you have another way to read the data as I want?

Cheers

Answer 1

[Image Analyst]

Try this:

% Generate some sample data:
tt = randi(3, 200, 3) 
% Get pairs of adjacent, consecutive rows each iteration.
for row = 1 : 2 : size(tt)
  subdata = tt(row:row+1, :)
  % Now do something with subdata.
end

Answer 2

[xueqi]

oh right. It acutally works in this way. I was missing multiplication syntax...