MINIMAL A-PRIORI ASSIGNMENT IN A DIRECT METHOD FOR DETERMINING PHENOMENOLOGICAL COEFFICIENTS UNIQUELY

We identify the coefficients of the transport equation in N dimensions grad c . grad h + c Delta h = d partial derivative h/partial derivati ve t + f by solving a differential system of the form grad c + ca = b. The assignment of c at one point only yields a unique solution, found by integration along arbitrary paths. This arbitrariness guarantees a good control of the error, notwithstanding the ill-posedness of the p roblem. For N = 2, the hypotheses allowing for this identification are satisfied when one knows two stationary potentials with non-overlappi ng equipotential lines and a third nonstationary one-this last needed only for determining d. The theory is applied to a numerical synthetic example, for various grid sizes or for noisy data. Notwithstanding th e minimal a priori information required for the coefficients, we are a ble to compute these at a large number of nodes with good precision. F or the sake of completeness, we give other results on identification.