user: Provide the full official documentation entry for Armature IK Panel, preserving all code examples.

assistant: This panel is used to select the IK Solver type for the armature: *Standard* or *iTaSC*.
Most the time people will use the *Standard* IK solver.

[image reference removed]

The armature IK panel.

### Standard

### iTaSC

iTaSC stands for instantaneous Task Specification using Constraints.

iTaSC uses a different method to compute the Jacobian, which makes it able to handle other constraints than
just end effectors position and orientation: iTaSC is a generic multi-constraint IK solver.
However, this capability is not yet fully exploited in the current implementation,
only two other types of constraints can be handled: Distance in the Cartesian space,
and Joint Rotation in the joint space. The first one allows maintaining an end effector
inside, at, or outside a sphere centered on a target position,
the second one is the capability to control directly the rotation of a bone relative to its parent.
Those interested in the mathematics can find a short description of the method used to build the Jacobian here.

iTaSC accepts a mix of constraints, and multiple constraints per bone:
the solver computes the optimal pose according to the respective weights of each constraint.
This is a major improvement from the current constraint system where constraints are solved
one by one in order of definition so that conflicting constraints overwrite each other.

Precision
:   The maximum variation of the end effector between two successive iterations
    at which a pose is obtained that is stable enough and the solver should stop the iterations.
    Lower values means higher precision on the end effector position.

Iterations
:   The upper bound for the number of iterations.

Solver
:   Selects the inverse Jacobian solver that iTaSC will use.

    SDLS
    :   Computes the damping automatically by estimating the level of ‘cancellation’ in the armature kinematics.
        This method works well with the Copy Pose constraint but has the drawback of damping more than
        necessary around the singular pose, which means slower movements.
        Of course, this is only noticeable in Simulation mode.

    DLS
    :   Computes the damping manually which can provide more reactivity and more precision.

        Damping Max
        :   Maximum amount of damping. Smaller values means less damping, hence more velocity
            and better precision but also more risk of oscillation at singular pose. 0 means no damping at all.

        Damping Epsilon
        :   Range of the damping zone around singular pose. Smaller values means a smaller zone
            of control and greater risk of passing over the singular pose, which means oscillation.

#### Animation

In Animation mode, iTaSC operates like an IK solver:
it is stateless and uses the pose from F-Curves interpolation as the start pose before the IK convergence.
The target velocity is ignored and the solver converges until the given precision is obtained.
Still the new solver is usually faster than the old one and provides features that are inherent to iTaSC:
multiple targets per bone and multiple types of constraints.

#### Simulation

The Simulation mode is the stateful mode of the solver: it estimates the target’s velocity,
operates in a ‘true time’ context, ignores rotation from keyframes
(except via a joint rotation constraint) and builds up a state cache automatically.

Reiteration
:   Never
    :   The solver starts from the rest pose and does not reiterate (converges) even for the first frame.
        This means that it will take a few frames to get to the target at the start of the animation.

    Initial
    :   The solver starts from the rest pose and re-iterates until the given precision is achieved,
        but only on the first frame (i.e. a frame which doesn’t have any previous frame in the cache).
        This option basically allows you to choose a different start pose than the rest pose
        and it is the default value. For the subsequent frames, the solver will track the target
        by integrating the joint velocity computed by the Jacobian solver over the time interval
        that the frame represents. The precision of the tracking depends on the feedback coefficient,
        number of substeps and velocity of the target.

    Always
    :   The solver re-iterates on each frame until the given precision is achieved.
        This option omits most of the iTaSC dynamic behavior: the maximum joint velocity
        and the continuity between frames is not guaranteed anymore in compensation of better
        precision on the end effector positions. It is an intermediate mode
        between *Animation* and real-time *Simulation*.

Auto Step
:   Use this option if you want to let the solver set how many substeps should be executed for each frame.
    A substep is a subdivision on the time between two frames for which the solver evaluates
    the IK equation and updates the joint position. More substeps means more processing but better precision
    on tracking the targets. The auto step algorithm estimates the optimal number of steps to get
    the best trade-off between processing and precision. It works by estimation of the nonlinearity
    of the pose and by limiting the amplitude of joint variation during a substep.
    It can be configured with next two parameters:

    Min
    :   Proposed minimum substep duration (in second).
        The auto step algorithm may reduce the substep further based on joint velocity.

    Max
    :   Maximum substep duration (in second). The auto step algorithm will not allow substep longer than this value.

Steps
:   If Auto Step is disabled, you can choose a fixed number of substeps with this parameter.
    Substep should not be longer than 10 ms, which means the number of steps is 4 for a 25 fps animation.
    If the armature seems unstable (vibrates) between frames,
    you can improve the stability by increasing the number of steps.

Feedback
:   Coefficient on end effector position error to set corrective joint velocity.
    The time constant of the error correction is the inverse of this value.
    However, this parameter has little effect on the dynamic of the armature
    since the algorithm evaluates the target velocity in any case.
    Setting this parameter to 0 means ‘opening the loop’:
    the solver tracks the velocity but not the position; the error will accumulate rapidly.
    Setting this value too high means an excessive amount of correction and risk of instability.
    The value should be in the range 20-100. Default value is 20, which means that tracking errors
    are corrected in a typical time of 100-200 ms.
    The feedback coefficient is the reason why the armature continues to move slightly
    in Simulation mode even if the target has stopped moving: the residual error
    is progressively suppressed frame after frame.

Max Velocity
:   Indicative maximum joint velocity in radian per second.
    This parameter has an important effect on the armature dynamic.
    Smaller value will cause the armature to move slowly and lag behind if the targets are moving rapidly.
    You can simulate an inertia by setting this parameter to a low value.