function error=bdfthre(dt,bigt,kbdf)
%dt=.2;
%bigt=1;
y(1)=1;
ye(1)=1;
t(1)=0;
thdt=(6/11)*dt;
%yold=y(1)+dt*(y(1)*y(1));
yold=1/(1-dt);
yoldr=1/(1-2*dt);
n=bigt/dt;
for i=1:n
  ynew=y(i);
  for m=1:kbdf
     ynew=(18/11)*y(i)-(9/11)*yold+(2/11)*yoldr-thdt*(ynew*ynew);
  end
  y(i+1)=ynew;
  yoldr= yold;
  yold=y(i);
  t(i+1)=t(i)+dt;
  ye(i+1)=1/(1+t(i+1));
  plot([0 bigt],[1 0],'.',t,y,'+',t,ye)
% semilogy([0 bigt],[1 0],'.',t,abs(y),'+',t,ye)
end
error=norm(y-ye,Inf);