Write a custom Field or Disturbance

Draft

This guide is scaffolded. The outline below marks what it should cover.

Most extensions are a new Disturbance on an existing Field — a new gravity source, a new flow. A genuinely new physical kind is a new Field subclass.

To cover

• New disturbance (common case) — subclass Disturbance, implement contribute_at_sym(point, t), set the combining flag (additive / averaged / baseline), add it to the field instance.
• Estimable disturbance — carry State / Noise declarations so the disturbance becomes an EKF-estimated state (as CraftWindBubble does).
• Body-anchored disturbance — emit it from a FieldSource part so it rides a craft.
• New field kind (rare) — subclass Field / SuperposedField, set value_shape (the CasADi-MX value type) and override _zero_value() (the additive identity); for compound combining, override value_at_sym() itself (see FluidField/FluidState).

Source material

• Reference: Fields
• Concepts: Fields and disturbances
• Code: manta/fields/base.py, manta/fields/gravity.py (simple disturbances), manta/fields/fluid.py (compound value)