The adsorption function. Mathematically, we view gas sensor arrays as mapping from gas composition space X := R G to sensor response space M := R M . The adsorption function a : x → m maps each gas composition vector x ∈ X to a sensor response vector m ∈ M. I.e., m = a(x) is a model for the total mass of gas adsorbed in each MOF (at thermodynamic equilibrium) as a function of the gas composition. We assume a(x) is a continuously differentiable function, disallowing adsorption/desorption hysteresis, gas-induced first-order structural transitions, chemical transformations, and condensation of adsorbates in the pores.