sft_wick.action — Action Definition

Action definition and multinomial expansion for perturbation theory.

class sft_wick.action.Action(vertices)

Bases: object

The interaction action \(S_{\mathrm{int}}\) as a sum of vertex terms.

The free action \(S_0\) is implicit — it defines the propagator rules (C and R). The Action stores only the interaction vertices.

Parameters:

vertices (list[Vertex]) – List of Vertex templates that make up \(S_{\mathrm{int}}\).

Variables:

vertices – The stored list of vertex templates.

all_vertex_combinations(order)

Generate all ways to pick order vertices (with repetition).

S_int^n = (v_0 + v_1 + …)^n expands via the multinomial theorem.

Yields:

(vertex_sequence, multinomial_coefficient) where vertex_sequence has length order and multinomial_coefficient = n! / (n_0! * n_1! * …).

Parameters:

order (int)

Return type:

Iterator[tuple[tuple[Vertex, …], int]]