Has anybody seen anything this expression before? Suppose that $z(\cdot)$ is the demand function of an individual (consumer/investor) and $p$ is the price of the commodity/asset demanded. Does anybody know what is the intuition behind the following expression?
\begin{align}pz^{'}(p)+z(p)\end{align}
It seems to me like the derivative of $(pz(p))^{'}$ with respect to $p$. What is the intuition behind this? Has anybody seen anything this expression before?
$p\cdot z(p)$ is total revenue (price times quantity), and so its derivative $\frac{\mathrm d}{\mathrm dp}pz(p)=pz'(p)+z(p)$ is marginal revenue.