function y=lagr1(x0,y0,x)
n=length(x0); m=length(x);
for i=1:m
   z=x(i);
   s=0.0;
   for k=1:n
      p=1.0;
      for j=1:n
         if j~=k
            p=p*(z-x0(j))/(x0(k)-x0(j));
         end
      end
      s=p*y0(k)+s;
   end
   y(i)=s;
end