# include "imfit.h"

float sersicTD (float, float, float *, int, float *);
void  sersicCL ();

void sersic_setup (char *name) {

  if (strcmp(name, "sersic")) return;

  fitfunc = sersicTD;
  cleanup = sersicCL;
  Npar = 8;
  Nfpar = 0;

  /* allocate free and fixed parameters */
  ALLOCATE (par, float, MAX (Npar, 1));
  bzero (par, Npar*sizeof(float));
  ALLOCATE (fpar, float, MAX (Nfpar, 1));
  bzero (fpar, Nfpar*sizeof(float));

  par[0] = get_variable_default ("Xg", 0);
  par[1] = get_variable_default ("Yg", 0);
  par[2] = 2.35 * sqrt(2.0) / get_variable_default ("SXg", 2.0);
  par[3] = 2.35 * sqrt(2.0) / get_variable_default ("SYg", 2.0);
  par[4] = 0.0;
  par[5] = get_variable_default ("Zpk", 10000);
  par[6] = get_variable_default ("Sg", 0.0);
  par[7] = get_variable_default ("Sr", 1.0);

  sky = &par[6];
}

/* sersic galaxy model -- x, y, sx, sy, sxy, I, sky, n */
/* exp (-b (r/r_e)^(1/n)) */
float sersicTD (float x, float y, float *par, int Npar, float *dpar) {

  float X, Y, px, py;
  float z, r, t, q, f;

  X = x - par[0];
  Y = y - par[1];
  
  px = par[2]*X;
  py = par[3]*Y;

  z = 0.5*SQ(px) + 0.5*SQ(py) + par[4]*X*Y;
  t = pow (z, par[7]);
  r = exp (-t);
  f = par[5]*r + par[6];
  q = par[5]*r*par[7]*pow(z, par[7]-1);

  if (dpar != NULL) {
    dpar[0] = q*(2*px*par[2] + par[4]*Y);
    dpar[1] = q*(2*py*par[3] + par[4]*X);
    dpar[2] = -2*q*px*X;
    dpar[3] = -2*q*py*Y;
    dpar[4] = -q*X*Y;
    dpar[5] = +r;
    dpar[6] = +1;
    dpar[7] = -q*log(z)*t;
  }
  return (f);
}

int sersicCL () {
  set_variable ("Xg",   par[0]);
  set_variable ("Yg",   par[1]);
  set_variable ("SXg",  2.35 * sqrt(2.0) / par[2]);
  set_variable ("SYg",  2.35 * sqrt(2.0) / par[3]);
  set_variable ("SXYg", par[4]);
  set_variable ("Zpk",  par[5]);
  set_variable ("Sg",   par[6]);
  set_variable ("Sr", par[7]);
}
