Overview
Given an operator {% O %} from Banach Spaces {% U %} and {% V %}
{% O:U \rightarrow V %}
and elements of {% U %} labeled {% x %} and {% t %}, the
Frechet Derivative {% T %} is an
operator
such that
{% \lim_{ ||t|| \to 0} \frac{|| O(x+t) - O(t) - T(t) ||}{||t||} = 0 %}
see Siddiqi