# field provider uniform_rotating

Describes the entry `uniform_rotating` at version `0.1.0`, registered by `mime.fields._uniform_rotating.UniformRotating`.

## At a glance

- field provider `uniform_rotating`, version `0.1.0`, namespace `mime`
- Nodes: [`UniformRotatingNode`](../../nodes/UniformRotatingNode.md)
- The equations are on the node page: [equations](../../nodes/UniformRotatingNode.md#governing-equations)
- Derivative: `exact`
- Validity: none declared

## What it models, and when not to use it

### A uniform field turning about an axis

**What it models.** A magnetic field that is the same at every point and turns right-handed about a fixed axis at a
commanded frequency, with a commanded amplitude: an idealisation of the field a rotating-magnet or coil rig makes over
a body small against it. `UniformRotating(rotation_axis=..., initial_direction=...)` as an apparatus's field, driven through its
two commands, `frequency` and `amplitude`. The field points along the initial direction, less its part along the axis,
at the start of the run. A reader's slot takes no points, since the field does not depend on them, and the gradient it
publishes is zero everywhere. Its time is the step count times the timestep, never a running sum of timesteps.

It publishes the flux density and the gradient, so it feeds `Magnetic.Torque` (which reads the flux density) and
`Magnetic.Force` (which reads the gradient, zero here, and so delivers nothing beside it).

**When not to use it.**
- Where the field varies across the body or with the body's place: a uniform field has no gradient, no pull and no
  near field. A source with a position, such as the point dipole, is the model for that.
- For a source that the body reacts on: this field has no source mounted anywhere, so it takes no reaction. A body's
  moment turns in it and the field is not turned back.
- For a frequency that changes during the run, taken as a sweep: the phase is the present frequency times the time since
  the start, not the integral of the frequency, so a change of frequency changes the phase at once, and the field's
  direction jumps with it. A frequency held constant, or changed where a jump of phase is acceptable, is what it is for.
- For a field's delivery by coils or magnets with a bandwidth, a lag, a saturation or a nonuniformity: it is the ideal
  field, and the commanded amplitude is the amplitude delivered. Nothing here bounds how far a rig's field is from that.

**Its derivative** is `exact`, as the generated section states.

**Versions.** `uniform_rotating` 0.1.0 is its first.

## Settings

| Setting | Type | Default | Dimension | Role | Default's kind |
|---|---|---|---|---|---|
| `initial_direction` | `Annotated[DirectionLike, Direction]` | `{"required": true}` | marked Direction | design | none |
| `rotation_axis` | `Annotated[DirectionLike, Direction]` | `{"required": true}` | marked Direction | design | none |

Each role and default's kind is the entry's `setting_roles` (`mime.registry.SettingRole`); a setting that declares none is required.

## Roles, reads and deliveries

Publishes:

| Interface | Output |
|---|---|
| [`field.magnetic.flux_density`](../../vocabulary.md#namespace-mime) | `flux_density` |
| [`field.magnetic.gradient`](../../vocabulary.md#namespace-mime) | `gradient` |

## Nodes it builds

- [`UniformRotatingNode`](../../nodes/UniformRotatingNode.md)

Declared in `builds`; the node walk compares it with what a round-trip case builds.

## Gradient status

The derivative through this entry is `exact`, the derivative of what it computes.

## Validity

none declared

## References

none declared

## Other declarations

| Class variable | Type | Value |
|---|---|---|
| `commands` | `ClassVar[Mapping[str, Command]]` | `` too long to show; see `mime registry --json` `` |
| `flags` | `ClassVar[frozenset[Capability]]` | `["provision=evaluated", "uniform"]` |
| `moving` | `ClassVar[bool]` | `false` |
| `outside_parts` | `ClassVar[bool]` | `false` |
| `parts` | `ClassVar[Mapping[str, str \| None]]` | `{}` |
| `turns_at` | `ClassVar[str \| None]` | `frequency` |