Mathc initiation/a287

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	x_dxdy.h

/* ---------------------------------- */
/* save as x_dxdy.h                   */
/* ---------------------------------- */
double int_dx(
double (*P_f)(double x, double y),

double (*Px0)(double y),
double (*Px1)(double y),
   int   nx,
   
double    y
)
{
   int i = 0;
double m = 0.;
double M = 0.;

 for(i = 0; i <= nx; i++)
 {
       if(i ==0 || i== nx){m = 1.;}
  else if(fmod(i,2) == 0 ){m = 2.;}
  else                    {m = 4.;}

  M += m * (*P_f)(((*Px0)(y)) + i*(((*Px1)(y))-((*Px0)(y)))/nx, y);
 }

  return( ((((*Px1)(y)) -((*Px0)(y)))*M) / (3*nx) );
}
/* ---------------------------------- */
double simpson_dxdy(
double (*P_f)(double x, double y),

double (*Px0)(double y),
double (*Px1)(double y),
   int   nx,
   
double   y0,
double   y1,
   int   ny
)
{
   int i = 0;
double m = 0.;
double M = 0.;

 for(i = 0; i <= ny; i++)
 {
       if(i ==0 || i== ny){m = 1.;}
  else if(fmod(i,2) == 0 ){m = 2.;}
  else                    {m = 4.;}

  M += m * int_dx((*P_f), (*Px0),(*Px1),nx, (y0+i*(y1-y0)/ny));
 }

  return( ((y1-y0)*M) / (3*ny) );
}
/* ---------------------------------- */
/* ---------------------------------- */