|
OpenSim
OpenSim 3.1
|
|
OpenSim
OpenSim 3.1
|
This class serves as a serializable FiberForceLengthCurve, commonly used to model the parallel elastic element in muscle models. More...
#include <FiberForceLengthCurve.h>
Public Member Functions | |
| FiberForceLengthCurve () | |
| The default constructor creates a fiber-force-length curve using the default property values and assigns a default name. | |
| FiberForceLengthCurve (double strainAtZeroForce, double strainAtOneNormForce, double stiffnessAtLowForce, double stiffnessAtOneNormForce, double curviness) | |
| Constructs a fiber-force-length curve using the provided parameters and assigns a default name. | |
| double | getStrainAtZeroForce () const |
| double | getStrainAtOneNormForce () const |
| double | getStiffnessAtLowForceInUse () const |
| double | getStiffnessAtOneNormForceInUse () const |
| double | getCurvinessInUse () const |
| bool | isFittedCurveBeingUsed () const |
| void | setCurveStrains (double aStrainAtZeroForce, double aStrainAtOneNormForce) |
| void | setOptionalProperties (double aStiffnessAtLowForce, double aStiffnessAtOneNormForce, double aCurviness) |
| double | calcValue (const SimTK::Vector &x) const override |
| Implement the generic OpenSim::Function interface. | |
| double | calcValue (double normFiberLength) const |
| Evaluates the fiber-force-length curve at a normalized fiber length of 'normFiberLength'. | |
| double | calcDerivative (double normFiberLength, int order) const |
| Calculates the derivative of the fiber-force-length multiplier with respect to the normalized fiber length. | |
| double | calcIntegral (double normFiberLength) const |
| Calculates the normalized area under the curve. | |
| SimTK::Vec2 | getCurveDomain () const |
| Returns a SimTK::Vec2 containing the lower (0th element) and upper (1st element) bounds on the domain of the curve. | |
| void | printMuscleCurveToCSVFile (const std::string &path) |
| Generates a .csv file with a name that matches the curve name (e.g., "bicepsfemoris_FiberForceLengthCurve.csv"). | |
| void | ensureCurveUpToDate () |
Property declarations | |
These are the serializable properties associated with this class. | |
| OpenSim_DECLARE_PROPERTY (strain_at_zero_force, double,"Fiber strain at zero force") | |
| OpenSim_DECLARE_PROPERTY (strain_at_one_norm_force, double,"Fiber strain at a tension of 1 normalized force") | |
| OpenSim_DECLARE_OPTIONAL_PROPERTY (stiffness_at_low_force, double,"Fiber stiffness at the end of the low-force region") | |
| OpenSim_DECLARE_OPTIONAL_PROPERTY (stiffness_at_one_norm_force, double,"Fiber stiffness at a tension of 1 normalized force") | |
| OpenSim_DECLARE_OPTIONAL_PROPERTY (curviness, double,"Fiber curve bend, from linear (0) to maximum bend (1)") | |
 Public Member Functions inherited from OpenSim::Function | |
| Function () | |
| Function (const Function &aFunction) | |
| virtual | ~Function () |
| virtual void | init (Function *aFunction) |
| Function & | operator= (const Function &aFunction) |
| virtual double | calcDerivative (const std::vector< int > &derivComponents, const SimTK::Vector &x) const |
| Calculate a partial derivative of this function at a particular point. | |
| virtual int | getArgumentSize () const |
| Get the number of components expected in the input vector. | |
| virtual int | getMaxDerivativeOrder () const |
| Get the maximum derivative order this Function object can calculate. | |
| virtual SimTK::Function * | createSimTKFunction () const =0 |
| Public Member Functions inherited from OpenSim::Object | |
| virtual | ~Object () |
| Virtual destructor for cleanup. | |
| virtual Object * | clone () const =0 |
| Create a new heap-allocated copy of the concrete object to which this Object refers. | |
| virtual const std::string & | getConcreteClassName () const =0 |
| Returns the class name of the concrete Object-derived class of the actual object referenced by this Object, as a string. | |
| virtual const VisibleObject * | getDisplayer () const |
| Methods to support making the object displayable in the GUI or Visualizer Implemented only in few objects. | |
| virtual VisibleObject * | updDisplayer () |
| get Non const pointer to VisibleObject | |
| bool | isEqualTo (const Object &aObject) const |
| Equality operator wrapper for use from languages not supporting operator overloading. | |
| Object & | operator= (const Object &aObject) |
| Copy assignment copies he base class fields, including the properties. | |
| virtual bool | operator== (const Object &aObject) const |
| Determine if two objects are equal. | |
| virtual bool | operator< (const Object &aObject) const |
| Provide an ordering for objects so they can be put in sorted containers. | |
| void | setName (const std::string &name) |
| Set the name of the Object. | |
| const std::string & | getName () const |
| Get the name of this Object. | |
| void | setDescription (const std::string &description) |
| Set description, a one-liner summary. | |
| const std::string & | getDescription () const |
| Get description, a one-liner summary. | |
| const std::string & | getAuthors () const |
| Get Authors of this Object. | |
| void | setAuthors (const std::string &authors) |
| Set Authors of this object, call this method in your constructor if needed. | |
| const std::string & | getReferences () const |
| Get references or publications to cite if using this object. | |
| void | setReferences (const std::string &references) |
| Set references or publications to cite if using this object. | |
| int | getNumProperties () const |
| Determine how many properties are stored with this Object. | |
| const AbstractProperty & | getPropertyByIndex (int propertyIndex) const |
| Get a const reference to a property by its index number, returned as an AbstractProperty. | |
| AbstractProperty & | updPropertyByIndex (int propertyIndex) |
| Get a writable reference to a property by its index number, returned as an AbstractProperty. | |
| bool | hasProperty (const std::string &name) const |
| Return true if this Object has a property of any type with the given name, which must not be empty. | |
| const AbstractProperty & | getPropertyByName (const std::string &name) const |
| Get a const reference to a property by its name, returned as an AbstractProperty. | |
| AbstractProperty & | updPropertyByName (const std::string &name) |
| Get a writable reference to a property by its name, returned as an AbstractProperty. | |
| template<class T > | |
| bool | hasProperty () const |
| Return true if this Object contains an unnamed, one-object property that contains objects of the given template type T. | |
| template<class T > | |
| const Property< T > & | getProperty (const PropertyIndex &index) const |
| Get property of known type Property<T> as a const reference; the property must be present and have the right type. | |
| template<class T > | |
| Property< T > & | updProperty (const PropertyIndex &index) |
| Get property of known type Property<T> as a writable reference; the property must be present and have the right type. | |
| void | setObjectIsUpToDateWithProperties () |
| When an object is initialized using the current values of its properties, it can set a flag indicating that it is up to date. | |
| bool | isObjectUpToDateWithProperties () const |
Returns true if no property's value has changed since the last time setObjectIsUpToDateWithProperties() was called. | |
| void | readObjectFromXMLNodeOrFile (SimTK::Xml::Element &objectElement, int versionNumber) |
| We're given an XML element from which we are to populate this Object. | |
| virtual void | updateFromXMLNode (SimTK::Xml::Element &objectElement, int versionNumber) |
| Use this method to deserialize an object from a SimTK::Xml::Element. | |
| virtual void | updateXMLNode (SimTK::Xml::Element &parent) |
| Serialize this object into the XML node that represents it. | |
| bool | getInlined () const |
| Inlined means an in-memory Object that is not associated with an XMLDocument. | |
| void | setInlined (bool aInlined, const std::string &aFileName="") |
| Mark this as inlined or not and optionally provide a file name to associate with the new XMLDocument for the non-inline case. | |
| std::string | getDocumentFileName () const |
| If there is a document associated with this object then return the file name maintained by the document. | |
| void | setAllPropertiesUseDefault (bool aUseDefault) |
| bool | print (const std::string &fileName) |
| Write this Object into an XML file of the given name; conventionally the suffix to use is ".osim". | |
| std::string | dump (bool dumpName=false) |
| dump the XML representation of this Object into an std::string and return it. | |
| void | clearObjectIsUpToDateWithProperties () |
| For testing or debugging purposes, manually clear the "object is up to
date with respect to properties" flag. | |
| virtual bool | isA (const char *type) const |
| The default implementation returns true only if the supplied string is "Object"; each Object-derived class overrides this to match its own class name. | |
| const std::string & | toString () const |
| Wrapper to be used on Java side to display objects in tree; this returns just the object's name. | |
| PropertySet & | getPropertySet () |
| OBSOLETE: Get a reference to the PropertySet maintained by the Object. | |
| const PropertySet & | getPropertySet () const |
Additional Inherited Members | |
| Static Public Member Functions inherited from OpenSim::Function | |
| static Function * | makeFunctionOfType (Function *aFunction, const std::string &aNewTypeName) |
| Static Public Attributes inherited from OpenSim::Object | |
| static const std::string | DEFAULT_NAME |
| Name used for default objects when they are serialized. | |
| Protected Member Functions inherited from OpenSim::Function | |
| void | resetFunction () |
| This should be called whenever this object has been modified. | |
| Protected Attributes inherited from OpenSim::Function | |
| SimTK::Function * | _function |
| Related Functions inherited from OpenSim::Object | |
| #define | OpenSim_DECLARE_CONCRETE_OBJECT(ConcreteClass, SuperClass) |
| Macro to be included as the first line of the class declaration for any non-templatized, concrete class that derives from OpenSim::Object. | |
| #define | OpenSim_DECLARE_ABSTRACT_OBJECT(ConcreteClass, SuperClass) |
| Macro to be included as the first line of the class declaration for any still-abstract class that derives from OpenSim::Object. | |
| #define | OpenSim_DECLARE_CONCRETE_OBJECT_T(ConcreteClass, TArg, SuperClass) |
| Macro to be included as the first line of the class declaration for any templatized, concrete class that derives from OpenSim::Object, like Set<T>. | |
| #define | OpenSim_DECLARE_ABSTRACT_OBJECT_T(ConcreteClass, TArg, SuperClass) |
| Macro to be included as the first line of the class declaration for any templatized, still-abstract class that derives from OpenSim::Object. | |
This class serves as a serializable FiberForceLengthCurve, commonly used to model the parallel elastic element in muscle models.
The fiber-force-length curve is dimensionless: force is normalized to maximum isometric force and length is normalized to resting fiber length. The user can adjust the maximum strain at no load and the strain developed under 1 normalized unit of force using the fitted curve. Additionally, if desired, it is possible to directly set the low-force stiffness of the fiber, the stiffness of the fiber at 1 normalized unit of force, and the shape of the curve (its 'curviness'):
| strainAtZeroForce | The fiber strain at which the fiber starts to develop force. strainAtZeroForce = 0.0 means that the fiber will begin developing tension when it is at its resting length. |
| strainAtOneNormForce | The fiber strain at which the fiber develops 1 unit of normalized force. strainAtOneNormForce = 0.6 means that the fiber will develop a tension of 1 normalized force when it is strained by 60% of its resting length or, equivalently, when it is stretched to 1.6 times its resting length. |
| stiffnessAtLowForce | The normalized stiffness (slope of the curve) when the fiber is just beginning to develop tensile force. |
| stiffnessAtOneNormForce | The normalized stiffness (slope of the curve) when the fiber develops a tension of 1 normalized unit of force. |
| curviness | A dimensionless parameter between 0 and 1 that describes the shape of the curve: a value of 0 indicates a curve that is very close to a straight line segment and a value of 1 indicates a curve that smoothly fills the corner formed by the linear extrapolation of 'stiffnessAtOneNormForce' and the x-axis, as shown in the figure. |
Note that we use the Cauchy or engineering definition of strain throughout: strain = (l-l0)/l0, where l is the current fiber length and l0 is its resting length.
Required Parameters
Optional Parameters
Conditions
strainAtZeroForce < strainAtOneNormForce stiffnessAtOneNormForce > 1/(strainAtOneNormForce-strainAtZeroForce) 0 < stiffnessAtLowForce < stiffnessAtOneNormForce 0 <= curviness <= 1
The required parameters can be set using either the constructor or the setCurveStrains function; the optional parameters can be set using the setOptionalProperties function. Note that filling in one optional parameter but not the others will throw an exception when the curve is built. The optional parameters can be used to vary the shape of the curve from a close approximation of a line to a sharply-bent curve.
The advantage of this curve over the typical exponential curve used in the literature is that it is continuous to the second derivative; the usual linearly-extrapolated exponential curve is only C0-continuous. The improved smoothness of this curve makes the equations somewhat easier to simulate and, more importantly, permits the use of derivative-based numerical methods on the curve. In addition, the extra parameters in this curve formulation can be adjusted to match a wide variety of shapes, should it be desired to fit the curve to a different set of experimental data.
Default Parameter Values If the optional parameters are not specified, the curve is fit to the experimentally measured fiber-force-length curves of Winters et al. (2010, Fig. 3a).
strainAtZeroForce .......... 0.0 strainAtOneNormForce ....... 0.7 stiffnessAtLowForce ........ 0.2 stiffnessAtOneNormForce .... 2.0 / (strainAtOneNormForce-strainAtZeroForce) = 2.86 curviness .................. 0.75
Example
Note that this object should be updated through the set methods provided. These set methods will take care of rebuilding the curve correctly. If you modify the properties directly, the curve will not be rebuilt, and upon calling a function like calcValue, calcDerivative, or printCurveToCSVFile, an exception will be thrown because the curve is out-of-date with its properties.
References
| OpenSim::FiberForceLengthCurve::FiberForceLengthCurve | ( | ) |
The default constructor creates a fiber-force-length curve using the default property values and assigns a default name.
| OpenSim::FiberForceLengthCurve::FiberForceLengthCurve | ( | double | strainAtZeroForce, |
| double | strainAtOneNormForce, | ||
| double | stiffnessAtLowForce, | ||
| double | stiffnessAtOneNormForce, | ||
| double | curviness | ||
| ) |
Constructs a fiber-force-length curve using the provided parameters and assigns a default name.
| double OpenSim::FiberForceLengthCurve::calcDerivative | ( | double | normFiberLength, |
| int | order | ||
| ) | const |
Calculates the derivative of the fiber-force-length multiplier with respect to the normalized fiber length.
| normFiberLength | The normalized length of the muscle fiber. |
| order | The order of the derivative. Only values of 0, 1, and 2 are acceptable. |
| double OpenSim::FiberForceLengthCurve::calcIntegral | ( | double | normFiberLength | ) | const |
Calculates the normalized area under the curve.
Since it is expensive to construct, the curve is built only when necessary.
| normFiberLength | The normalized length of the muscle fiber. |
|
inlineoverridevirtual |
Implement the generic OpenSim::Function interface.
Reimplemented from OpenSim::Function.
| double OpenSim::FiberForceLengthCurve::calcValue | ( | double | normFiberLength | ) | const |
Evaluates the fiber-force-length curve at a normalized fiber length of 'normFiberLength'.
| void OpenSim::FiberForceLengthCurve::ensureCurveUpToDate | ( | ) |
| SimTK::Vec2 OpenSim::FiberForceLengthCurve::getCurveDomain | ( | ) | const |
Returns a SimTK::Vec2 containing the lower (0th element) and upper (1st element) bounds on the domain of the curve.
Outside this domain, the curve is approximated using linear extrapolation.
| double OpenSim::FiberForceLengthCurve::getCurvinessInUse | ( | ) | const |
| double OpenSim::FiberForceLengthCurve::getStiffnessAtLowForceInUse | ( | ) | const |
| double OpenSim::FiberForceLengthCurve::getStiffnessAtOneNormForceInUse | ( | ) | const |
| double OpenSim::FiberForceLengthCurve::getStrainAtOneNormForce | ( | ) | const |
| double OpenSim::FiberForceLengthCurve::getStrainAtZeroForce | ( | ) | const |
| bool OpenSim::FiberForceLengthCurve::isFittedCurveBeingUsed | ( | ) | const |
| OpenSim::FiberForceLengthCurve::OpenSim_DECLARE_OPTIONAL_PROPERTY | ( | stiffness_at_low_force | , |
| double | , | ||
| "Fiber stiffness at the end of the low-force region" | |||
| ) |
| OpenSim::FiberForceLengthCurve::OpenSim_DECLARE_OPTIONAL_PROPERTY | ( | stiffness_at_one_norm_force | , |
| double | , | ||
| "Fiber stiffness at a tension of 1 normalized force" | |||
| ) |
| OpenSim::FiberForceLengthCurve::OpenSim_DECLARE_OPTIONAL_PROPERTY | ( | curviness | , |
| double | , | ||
| "Fiber curve | bend, | ||
| from linear(0) to maximum bend(1)" | |||
| ) |
| OpenSim::FiberForceLengthCurve::OpenSim_DECLARE_PROPERTY | ( | strain_at_zero_force | , |
| double | , | ||
| "Fiber strain at zero force" | |||
| ) |
| OpenSim::FiberForceLengthCurve::OpenSim_DECLARE_PROPERTY | ( | strain_at_one_norm_force | , |
| double | , | ||
| "Fiber strain at a tension of 1 normalized force" | |||
| ) |
| void OpenSim::FiberForceLengthCurve::printMuscleCurveToCSVFile | ( | const std::string & | path | ) |
Generates a .csv file with a name that matches the curve name (e.g., "bicepsfemoris_FiberForceLengthCurve.csv").
This function is not const to permit the curve to be rebuilt if it is out-of-date with its properties.
| path | The full destination path. Note that forward slashes ('/') must be used and there should not be a slash after the last folder. |
The file will contain the following data:
column: 1 | 2 | 3 | 4 data: x | y | dy/dx | d2y/dx2
Samples will be taken from the zero-force region, through the curve, out to strains beyond which the fiber generates passive normalized forces greater than 1. The curve is sampled quite densely: the fiber-force-length .csv file will have 200+20 rows.
Example To read the .csv file into Matlab, you need to set csvread to ignore the header row. Since csvread is 0-indexed, the following example will begin reading the .csv file from the first column of the second row:
data = csvread('bicepsfemoris_FiberForceLengthCurve.csv', 1, 0);
| void OpenSim::FiberForceLengthCurve::setCurveStrains | ( | double | aStrainAtZeroForce, |
| double | aStrainAtOneNormForce | ||
| ) |
| aStrainAtZeroForce | The fiber strain at which the fiber starts to develop force. strainAtZeroForce = 0.0 means that the fiber will begin developing tension when it is at its resting length. |
| aStrainAtOneNormForce | The fiber strain at which the fiber develops 1 unit of normalized force. strainAtOneNormForce = 0.6 means that the fiber will develop a tension of 1 normalized force when it is strained by 60% of its resting length or, equivalently, when it is stretched to 1.6 times its resting length. |
Conditions
strainAtZeroForce < strainAtOneNormForce
| void OpenSim::FiberForceLengthCurve::setOptionalProperties | ( | double | aStiffnessAtLowForce, |
| double | aStiffnessAtOneNormForce, | ||
| double | aCurviness | ||
| ) |
| stiffnessAtLowForce | The normalized stiffness (slope of the curve) when the fiber is just beginning to develop tensile force. |
| stiffnessAtOneNormForce | The normalized stiffness (slope of the curve) when the fiber develops a tension of 1 normalized unit of force. |
| curviness | A dimensionless parameter between 0 and 1 that controls the shape of the curve: a value of 0 will create a curve that is very close to a straight line segment and a value of 1 will create a curve that smoothly fills the corner formed by the linear extrapolation of 'stiffnessAtOneNormForce' and the x-axis, as shown in the figure in the class description. |
Conditions
stiffnessAtOneNormForce > 1/(strainAtOneNormForce-strainAtZeroForce) 0 < stiffnessAtLowForce < stiffnessAtOneNormForce 0 <= curviness <= 1
1.8.1.2