// poisson-kikuchi-square.edp
// https://m-katsurada.sakura.ne.jp/program/fem/poisson-kikuchi-square.edp
// 菊地文雄, 有限要素法概説, サイエンス社

int m=10;
mesh Th=square(m,m);
// plot(Th,wait=true,ps="Th.eps");
savemesh(Th,"Th.msh");
fespace Vh(Th,P1);
Vh u,v;
func f=1;
func g1=0;
func g2=0;
solve Poisson(u,v)=
  int2d(Th)(dx(u)*dx(v)+dy(u)*dy(v))
 -int2d(Th)(f*v)
 -int1d(Th,2,3)(g2*v)
 +on(1,4,u=g1);
plot(u,wait=1,ps="poisson-kikuchi-square.eps");

//3次元鳥瞰図
//real [int] levels =0.0:0.01:1.0;
//plot(u,dim=3,viso=levels,fill=true,wait=true);