about moving datacursor in color plot

I am using matlab to plot a false color map and trigger the data cursor, I found that if the map is n-by-n (square), I can use the up/down/left/right arrow to move the data cursor to the next point and show the tip, but if the map is not square (n-by-m), then using up/down still can move it up or down but pressing left or right will cause the data cursor jumping, why's that?

function MyMain
  M=rand(400, 600); 
  pcolor(M); 
  shading flat;

    cursorMode = datacursormode(gcf);
    datacursormode on;
    set(cursorMode, 'UpdateFcn', {@myupdate, M});  
  end

function output_txt = myupdate(obj, event_obj, M)
  pos = get(event_obj,'Position');
  idx = get(event_obj, 'DataIndex');
  val = M(idx);
  output_txt = {['X: ',num2str(pos(1),10)], ['Y: ',num2str(pos(2),10)]};

    if length(pos) > 2
      val = M(idx);
      output_txt{end+1} = ['VAL: ',num2str(val, 10)];
    end
  end

By the way, in above code, I pass the map to the callback function so to show the value at current position, but it is so slow if the data is big. Any way to the data cursor tip refer to the value without passing the whole matrix? Thanks.

Answer 1

[Walter Roberson]

For the second point, use a nested function that has access to M.

[Ki]

Hi Walter, Thanks for your reply. What does it mean by using nested function?