function y = bspline(x,i,t)

n=length(x);

if t <x(i) | t > x(i+4)
   y = 0;
   return
end

y=0;
for j=i:i+4
  p = 1;
  for l=i:i+4
    if l ~= j
       p = p * (x(j)-x(l));
    end
  end

  y = y + step_cubic(t,x(j))/p;
end
  y = y * (x(i+4)-x(i));