function y=einstein(x)
sx=size(x,1);
for n=1:sx
  if abs(x(n))<1
    term=x(n);
    k=1; s0=0; s1=x(n);
    while s1~=s0
      k=k+1;
      s0=s1;
      term=-x(n)*term/k;
      s1=s0+term;
    end
    y(n)=x(n)/s1;
  else
    y(n)=x(n)/(1-exp(-x(n)));
  end
end
y=y';
