function r=rot4y(theta)
% r = roty(theta)
%
% roty produces a 4x4 rotation matrix representing
% a rotation by theta radians about the y axis.
%
%	Argument definitions:
%	
%	theta = rotation angle in radians
c = cos(theta);
s = sin(theta);
r = [c  0  s 0;
     0  1  0 0;
    -s  0  c 0;
     0  0  0 1];
