  In the framework of risk management, for the study of the sensitivity of
pricing and hedging in stochastic financial models to changes of parameters and
to perturbations of the stock prices, we propose an error calculus which is an
extension of the Malliavin calculus based on Dirichlet forms. Although useful
also in physics, this error calculus is well adapted to stochastic analysis and
seems to be the best practicable in finance. This tool is explained here
intuitively and with some simple examples.
