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