|
Simbody
3.4 (development)
|
|
Simbody
3.4 (development)
|
(CAUTION: still under development) This is a Measure whose value at time t is the value that its source operand had at time t-delay for a specified delay. More...
#include <Measure.h>
Inheritance diagram for SimTK::Measure_< T >::Delay:Classes | |
| class | Implementation |
Public Member Functions | |
| Delay (Subsystem &sub, const Measure_< T > &source, Real delay) | |
| Create a Measure whose output is the same as the given source measure but delayed by a time delay. | |
| Delay & | setUseLinearInterpolationOnly (bool linearOnly) |
| (Advanced) Restrict the Delay measure to use only linear interpolation to estimate delayed values. | |
| Delay & | setCanUseCurrentValue (bool canUseCurrentValue) |
| (Advanced) Allow the Delay measure to refer to the current value when estimating the delayed value. | |
| Delay & | setSourceMeasure (const Measure_< T > &source) |
| Replace the source measure. | |
| Delay & | setDelay (Real delay) |
| Change the delay time. | |
| bool | getUseLinearInterpolationOnly () const |
| Return the value of the "use linear interpolation only" flag. | |
| bool | getCanUseCurrentValue () const |
| Return the value of the "can use current value" flag. | |
| const Measure_< T > & | getSourceMeasure () const |
| Obtain a reference to the source Measure. | |
| Real | getDelay () const |
| Get the amount of time by which this Measure is delaying its source Measure. | |
(CAUTION: still under development) This is a Measure whose value at time t is the value that its source operand had at time t-delay for a specified delay.
For times prior to the start of a simulation this Measure behaves as though the source value had been constant at its initial value.
When the source Measure can provide a time derivative dvalue we use saved (t,value,dvalue) triples surrounding the required time to construct a cubic Hermite interpolant giving a third-order accurate estimate of the delayed value. Otherwise we use more data points to construct the cubic interpolant but the accuracy cannot be guaranteed. If there aren't enough data points, then linear interpolation is used instead. There is an option to force use of linear interpolation if you prefer.
In the case where the delayed time is within the current step, we would need the current source value in order to interpolate. We assume that is not available (commonly the current value depends on the delayed value) so have to extrapolate beyond the last buffered value in that case. Extrapolation is considerably less accurate than interpolation, so when step sizes are large compared to delay times the accuracy of the delayed value is reduced. In cases where the source does not depend on its delayed value, you can request that the current value be used if necessary, ensuring consistent accuracy. Alternatively, you can set the maximum integrator step size to be just less than the minimum delay time, guaranteeing that there will always be an entry already in the buffer that is later than any requested delayed time. That could have a substantial performance penalty if steps much larger than the delay would otherwise have been taken.
This Measure maintains a variable-sized buffer holding values that the source measure and its time derivative (if available) had at each time step starting just prior to t-delay until just before the current time t. New values are added to the end of the buffer as integrator steps are completed, and old values that are no longer needed are removed from the beginning. When a value is requested at current time t, the Measure interpolates using values from just prior to t-delay and just afterwards to approximate the value at t-delay.
| SimTK::Measure_< T >::Delay::Delay | ( | Subsystem & | sub, |
| const Measure_< T > & | source, | ||
| Real | delay | ||
| ) | [inline] |
Create a Measure whose output is the same as the given source measure but delayed by a time delay.
| Delay& SimTK::Measure_< T >::Delay::setUseLinearInterpolationOnly | ( | bool | linearOnly | ) | [inline] |
(Advanced) Restrict the Delay measure to use only linear interpolation to estimate delayed values.
By default it uses cubic interpolation whenever possible. Cubic interpolation will almost always be better but can be unstable in some circumstances. Despite its name this flag also applies to extrapolation if we have to do any. This is a topological change.
| Delay& SimTK::Measure_< T >::Delay::setCanUseCurrentValue | ( | bool | canUseCurrentValue | ) | [inline] |
(Advanced) Allow the Delay measure to refer to the current value when estimating the delayed value.
Normally we expect that the current value might depend on the delayed value so is not available at the time we ask for the delayed value. That means that if the delayed time is between the current time and the last saved time (that is, it is a time during the current integration step), the measure will have to extrapolate from the last-saved values to avoid requiring the current value to be available. With this approach the "depends on" time for a Delay measure is just Time stage since it does not depend on any current calculations. However, extrapolation is much less accurate than interpolation so if you don't mind the "depends on" stage for a Delay measure being the same stage as for its source measure, then you can get nicer interpolated values. This is a topological change.
| Delay& SimTK::Measure_< T >::Delay::setSourceMeasure | ( | const Measure_< T > & | source | ) | [inline] |
Replace the source measure.
This is a topological change.
| Delay& SimTK::Measure_< T >::Delay::setDelay | ( | Real | delay | ) | [inline] |
Change the delay time.
This is a topological change.
| bool SimTK::Measure_< T >::Delay::getUseLinearInterpolationOnly | ( | ) | const [inline] |
Return the value of the "use linear interpolation only" flag.
| bool SimTK::Measure_< T >::Delay::getCanUseCurrentValue | ( | ) | const [inline] |
Return the value of the "can use current value" flag.
| const Measure_<T>& SimTK::Measure_< T >::Delay::getSourceMeasure | ( | ) | const [inline] |
Obtain a reference to the source Measure.
| Real SimTK::Measure_< T >::Delay::getDelay | ( | ) | const [inline] |
Get the amount of time by which this Measure is delaying its source Measure.
1.7.6.1 
