problem of cursor position

[Han Xu]

Hi,

Suppose my current emacs window is like this:
---------------------------------------------
Line 1
...
..
Line 20
....
....
Line 40
----------------------------------------------

where, Line 40 is at bottom of the window. Now, I press the "Down" arrow
key, by which I intend to move to next line, i.e. Line 41. AND: I intend
to make the Line 41 at the bottom of the window, NOT at the middle of
window, which is default by Emacs. How can I achieve that ?

i.e. I want the result like this:
--------------------------------
Line 2
...
...
Line 21
...
...
Line 41
--------------------------------

NOT like this:
---------------------------------
Line 20
...
...
Line 41
...
...
Line 61
----------------------------------

Thanks a lot !

Han