// F(X) = 1 / (1 + exp(-X)) = logit(X), F'(X) = logit(X) * (1 - logit(X))
private static FNode GradientOfLogit(FNode Node, FNodePointer X)
{
// Logit, create two to avoid incest in the node tree //
FNode t = X.CloneOfMe();
FNode u = X.CloneOfMe();
FNode v = FNodeFactory.Value(1D);
return t * (v - u);
}
