// example27.edp, from chap3/convects.edp
// Characteristics Galerkin
border C(t=0, 2*pi) { x=cos(t);  y=sin(t); };
mesh Th = buildmesh(C(100));
fespace Uh(Th,P1);
Uh cold, c = exp(-10*((x-0.3)^2 +(y-0.3)^2));

real dt = 0.17,t=0;
Uh u1 = y, u2 = -x;

real [int] viso=[-0.1, 0, 0.5, 0.1, 0.5, 0.2, 0.25, 0.3, 0.35, 0.4, 
                 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.9, 1];

for (int m=0; m<2*pi/dt ; m++) {
    t += dt;     
    cold=c;
    c=convect([u1,u2], -dt, cold);
    plot(c,cmm=" t="+t + ", min=" + c[].min + ", max=" +  c[].max, 
         viso=viso, dim=3, fill=true);
}
plot(c,wait=true,fill=false,value=true,viso=viso,
  cmm="example27, min=" + c[].min + ", max=" +  c[].max);