A simple algorithm for automatic Feynman diagram generation Original Research Article

We present an algorithm for automatic Feynman diagram (FD) generation. Derived directly from the definition formula of an FD, the algorithm features first of all a clear concept. Also, it could naturally generate the symmetry factor for each FD. As it is free of complex and tricky operations commonly seen in other FD generation software, the code for this algorithm should always be easy to write. We provide such an implementation in C. This C program is very small, but it is fast and powerful; it receives as input an arbitrary user-defined model and an arbitrary process, and generates FDs at any order. In its current status the algorithm suppresses the equivalent FDs at one-loop order totally; but at two-loop or higher order the suppression is incomplete, although this fact does not hurt the correctness of the Feynman amplitudes obtained. We expect the algorithm to be convenient for researchers studying new calculation techniques or building new calculation tools, and for those who are working on effective field theory.