1. A simulating machine ( 100 ) for simulating a system having a system output (V) influenced by system parameters (θ), the simulating machine ( 100 ) comprising: a sample generating unit ( 101 ) configured to provide samples (X) of system components influenced by said parameters (θ); a differentiator ( 150 ) coupled to said sample generating unit ( 101 ) and configured to operate on said samples (X) in accordance with an adjoint of a function (P(X,θ)) defining said output V in terms of a relationship between said components, the simulating machine ( 100 ) thereby enabling sensitivities (dV/d θ) of said system output (V) to be determined with respect to said parameters (θ).