/**
# Diffusive tracer, vof tracer and particle tracers.

The case is based on a [test case](/src/test/revered/c) for the `vof`
advection. Results are visual:

![Swirling tracers](reversed/mov.mp4)

![The Magenta circle is the exact solution](reversed/result.png)
 */

#include "advection.h" //diffusive tracer field
#include "vof.h"       //Interface tracer
#include "view.h"
#define BVIEW 1
#include "particles.h" //Particles


scalar f[], s[], * interfaces = {f}, * tracers = {s};

double T = 15;
int main () {
 L0 = 1;
  X0 = Y0 = -L0/2;
  DT = 0.1;
  N = 64;
  P_RK3 = true; // <- this improved the result considerably
  run();
}

#define circle(x,y) (sq(0.2) - (sq(x + 0.2) + sq(y + .236338)))

event init (t = 0) {
  fraction (f, circle(x,y));   // 1 line for initialization
  foreach()
    s[] = exp(10*circle(x,y)); // 2 lines

  n_part = 100;
  loc = malloc (sizeof(coord)*n_part);  //5 lines
  foreach_particle() {
    p_x() = -0.2 + 0.2*sin((double)j);
    p_y() = -0.236338 + 0.2*cos((double)j);
  }
}

event velocity (i++) {
  vertex scalar psi[];
  foreach_vertex()
    psi[] = - 1.5*sin(2.*pi*t/T)*sin((x + 0.5)*pi)*sin((y + 0.5)*pi)/pi;
  trash ({u});
  struct { double x, y; } f = {-1.,1.};
  foreach_face()
    u.x[] = f.x*(psi[0,1] - psi[])/Delta;
  boundary ((scalar *){u});
}

event movie (t += 0.1) {
  draw_vof("f");
  squares ("s");
  scatter (loc);
  save ("mov.mp4");
}

event stop (t = T) {
  scalar b[];
  fraction (b, circle(x,y));
  draw_vof("b", lc = {1,0,1}, lw = 2);
  draw_vof("f");
  squares ("s");
  translate (z = 0.01)
    scatter (loc_n);
  save ("result.png");
}