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This tutorial talks about extracting the far-field-map from the numerical
solution of a Helmholtz or a Schroedinger problem solved on a finite numerical
box. We try to make the connection between imaging concepts, traditionally
described by the Helmholtz equation and the equivalent concepts in the
Schroedinger equation.**

In scattering calculations of atomic and molecular processes it is relatively straightforward to obtain a high dimensional wave function describing the scattering. Extracting the cross section of the various processes from that wave function is, in contrast, a delicate matter.

We give a tutorial in extracting the amplitudes from wave functions. We start from the Helmholtz equation and we slowly evolve to more complicated atomic and molecular processes.

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