Projection onto orthogonal basis j =(0,1) v =(v ,v ) x y p ij p uv u=(u ,u ) y x i =(1,0) p = (5,4) p = (u·p , v·p ) ij ij uv ij u u  5  u u  p =  x x    =  x y  p ij uv  v y v y   4   v x v y