ABSTRACT

In order to minimize ?2, replace D(v) with D(v) +eh(v), where h(v) is an arbitrary function not identically equal to zero and e is small positive constant. Just as we find an extremum of a real function h(t) by taking the derivative with respect to t and setting it equal to zero, we can replace D with D+eh and differentiate with respect to e:

Now

Since e is very small, we ignore terms proportional to e2. Some more manipulation yields