format long
x = [0.3 0.4 0.5 0.6];
e = [exp(-2*x(1)) exp(-2*x(2)) exp(-2*x(3)) exp(-2*x(4))];
y = 0.426297847487559;
n = 4;
P = 0;
for i = 1 : n
  L(i) = 1;
  for j = 1 : n
    if( i~=j)
      L(i) = L(i)*(y-x(j))/(x(i)-x(j));
     end
   end
   P = P + e(i)*L(i);
 end
   P