function [xp,yp,zp] = rot(x,y,z,inc,omega);
% [xp,yp,zp] = rot(x,y,z,inc,omega);
% takes vectors x,y,z and transforms them
% rotates through angle of nodes omega
% tilts through inclination inc
% evaluate trig functions once:
	cosomega = cos(omega);
	sinomega = sin(omega);
	cosinc = cos(inc);
	sininc = sin(inc);
% transform:
% tilt by inclination angle around x axis
% since perihelion is defined in generating ellipse
% with ellip.m, node is on x-axis.
% recall that argument of perihelion is defined from node
	xt = x;
	yt = y*cosinc - z*sininc;
	zt = z*cosinc + y*sininc;
% these are NOT new axes, but the vectors themselves are 
% rotated in ecliptic coordinates.  Thus, the next 
% transformation is truly about the z-axis, as it should
% be.  It is NOT about a rotated z-axis.  Think of 
% transforming components, not basis vectors.

% rotate around z axis by omega 
	xp = xt*cosomega - yt*sinomega;
	yp = yt*cosomega + xt*sinomega;
	zp = zt;