Logarithmic differentiation
= Logarithmic differentiation
{title2=$\frac{d}{dx}\log|f(x)|=f'(x)/f(x)$}
Apply the <chain rule> to the <logarithm> of a differentiable nonzero real-valued <function>. This converts products into sums and powers into multiplicative coefficients. In particular, for positive $f=C\prod_i x_i^{a_i}$, $df/f=\sum_i a_i\,dx_i/x_i$. It is useful for <monomial uncertainty propagation> and for finding relative rates of change.