/* Last edited on 2008-01-24 18:45:13 by lhf */

static void f(real* x, real* y)
{
 real X=*x;
 real Y=*y;
#if 1
	*x = Y-0.5*Y*(1-X*X-Y*Y);
	*y = -X;
#endif
#if 0
	*x = Y+0.5*(1-X*X-Y*Y);
	*y = -X;
#endif
#if 0
	if (Y<(X/2))    { *x=0.5+X/2; *y=2*Y; }
	else if (Y<X)   { *x=0.5+Y-X; *y=X;   }
	else if (Y<2*X) { *x=X-Y/2;   *y=Y;   }
	else            { *x=0.5-Y/2; *y=2*X; }
#endif
#if 0
 *x=Y;
 *y=1-X;
#endif
#if 0
 *x=Y+2*Y*(1-Y)*X*(1-X);
 *y=1-X;
#endif
#if 0
 *x=1.0-a*X*X+Y;
 *y=b*X;
#endif
}