Assg. $7\mathrm{.}2($bonus: $2+1$ pts$).,$ For a surface $S$ represented by $r(u,v)$ with uin$[a,b]$&vin$[c,d]$

$($rectangular region$),$ we get easily a poygon mesh using the vertices $V_{k,l}$:$=r(u_k,v_l)$ for $0km$&

$0ln$ and the partitions $V_{k,l}{E}_{H,k,l}a=u_0.$

$(a)$ Describe a polygon mesh with the vertices $V_{k,l}by$ giving a list $of$ edges and faces.

Hint: $It$ might $be$ useful $to$ use triple indices for edges and faces $(e.g.E_{H,k,l}$ for "horizontal" edges$).$

$(b)$ Find a formula $to$ calculate a normal vector for each face.