# POINCARE_OUTPUT

Specifies parameters for the output of the Poincare plane sections.

## Type

AcuTrace Command

## Syntax

POINCARE_OUTPUT {parameters}

## Qualifier

This command has no qualifier.

## Parameters

- active (boolean) [=off]
- Flag specifying if Poincare output is active.
- poincare_sections or psections (array) [={}]
- Definition of the Poincare section rectangles. Each row is of the form x1, y1, z1,x2 ,y2 ,z2, x3, y3, z3 and defines a rectangle by the prescription given below.
- flow_state_data or flow_state (boolean) [=off]
- Flag specifying whether to include the flow state in the output.
- flow_gradient_data or flow_gradient (boolean) [=off]
- Flag specifying whether to include gradients of the flow state in the output.

## Description

Particle traces are computed by AcuTrace as a series of segments. Poincare plane output is written only when a particle path crosses through and inside of a Poincare section rectangle. The particle path is interpolated between the segment endpoints that are on either side of the rectangle.

The Poincare section rectangles are defined by three points as follows: the first two points define one edge of the rectangle, and the third point is projected to the closest plane that is normal to this edge and passes through one of the first two points. The fourth point is constructed to finish the rectangle. In the simplest case, the three points can be three of the vertices of the rectangle.

```
POINCARE_OUTPUT {
active = on
poincare_sections = { .5587, -10.0, -10.0,
.5587, -10.0, 10.0,
.5587, 10.0, -10.0 ;
-.0499, -10.0, -10.0,
-.0499, -10.0, 10.0,
-.0499, 10.0, -10.0 ;
}
...
}
```

The active, flow_state_data, and flow_gradient_data parameters control what information is recorded. No trace output is recorded unless active = on. By default, all particle outputs and no flow outputs are recorded when trace output is active.

Particle values are the state of the particle, that is, its position, time, particle velocity, and so on. The flow outputs are found by interpolating the AcuSolve flow field to the current position and time of the particle.

Particle outputs always include

- Seed ID
- Coordinates
- Time
- Particle velocity
- Element ID
- Element set ID
- Marker
- Particle velocity magnitude
- Trace length

They also include

- Particle mass
- Particle density
- Particle radius

if the parameter particle equals finite_mass model in the EQUATION command,

- Component values

if the parameter number_particle_components in the EQUATION command is non-zero,

- User equation values

if one or more user equations are specified by the user_equations parameter of the EQUATION command.

- Turbulence random seed

if the parameter turbulent_trace equals on in the TRACE_PARAMETERS command and

- Stretch vector
- Stretch magnitude
- Log stretch magnitude
- Stretch rate magnitude

if the parameter stretch does not equal none in the EQUATION command.

Flow state values always include

- Flow velocity
- Flow pressure
- Flow velocity magnitude
- Flow strain rate magnitude

They also include

- Flow temperature
- Flow species
- Flow eddy viscosity

if these are available in the AcuSolve database.

Flow gradient values currently include only

- Gradient of flow velocity

Note that for the massless particle motion equation, the particle and the flow velocity fields are identical except possibly for particle positions in elements next to a wall.