/* the pendulum eqns */

float  F(t, y,  i) 

     float      t, *y;
     int        i;

{

switch (i)
    {
    case 0 :
      return(y[1]);
      break;
    case 1 :
      return(-sqr(omega)*y[0]); 
      break; 
  
    }
}