function [t,y]=multiex(a,b,eta,N,iex)
h=(b-a)/N;
t=a:h:b;
k=input('Input k, the step number of the method ')
alphas=input('Input [alpha_0 alpha_1 ... alpha_(k-1)] ')
betas=input('Input [beta_0 beta_1 ... beta_(k-1)] ')

if iex==1 
  for j=1:k
     y(j)=yexact(a+(j-1)*h);
  end 
else
  y(1:k)=input('Input [y_0 y_1 ... y_(k-1)] ');
end
y=y';

for i=1:k
  fn(i,1)=f(t(i),y(i));
end

for n=k:N  
   oldy=y(n+1-k:n);
   oldf=fn(n+1-k:n); 
   y(n+1)=-alphas*oldy+h*(betas*oldf);
   fn(n+1)=f(t(n+1),y(n+1));
end


