sofia.field.neighbour_sum

class sofia.field.neighbour_sum.NeighbourSum(*args)

Bases: Function

Sum a per-pair expression over the neighbours of each particle.

Parameters:

• expr – Per-pair expression. field is the value at the particle itself, field.neighbour the value at the neighbour. Can be scalar or vector.

• pos – Particle position, determines which particles count as neighbours.

• h – Cutoff radius, only pairs closer than h contribute to the sum.

• exclude_self – If True, skip the particle itself. Only for sums over the same domain.

• neighbours – Positions of the particles to sum over, on this or another particle domain. Defaults to pos. In a sum over another domain, fields of that domain are the values at the neighbour. .neighbour is only needed when both are on the same domain.

property cutoff: Basic

Condition for a neighbour to contribute to the sum.

A neighbour contributes if it is closer than h to the particle.