**Physical applications of group theory**

**Abstract:**

In testing a nuclear problem, we encounter the following problem. In order to assess the accuracy of a computer
modell, results of the modell should be compared to measurements. But measurements are carried out in a smaller and simpler
reactor. We address the problem how to project the measured values in a given geometry to another geometry.

We distingush three cases.

Case A. Geometries mapped into each other by symmetries of the equation. This case is well known.

Case B. Geometries where transplantation is possible. In that case every solution can be transplanted.

Case C. Geometries where no transplantation is possible, then the fundamental solution associated with the so called
dominant eigenvalue can be transformed to the other geometry.

Simple applications will be included. We strongly believe that our idea will turn a new page in testing computer codes.

Joint work with *M. Antal*.