API  4.2 For C++ developers
OpenSim::FiberForceLengthCurve Class Reference

This class serves as a serializable FiberForceLengthCurve, commonly used to model the parallel elastic element in muscle models. More...

Inheritance diagram for OpenSim::FiberForceLengthCurve:

## OpenSim Properties, Sockets, Outputs, Inputs

Properties (single-value)
double strain_at_zero_force
"Fiber strain at zero force" More...

double strain_at_one_norm_force
"Fiber strain at a tension of 1 normalized force" More...

Properties (optional)
double stiffness_at_low_force
"Fiber stiffness at the end of the low-force region" More...

double stiffness_at_one_norm_force
"Fiber stiffness at a tension of 1 normalized force" More...

double curviness
"Fiber curve bend, from linear (0) to maximum bend (1)" More...

## Public Member Functions

FiberForceLengthCurve ()
The default constructor creates a fiber-force-length curve using the default property values and assigns a default name. More...

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. More...

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 stiffnessAtLowForce, double stiffnessAtOneNormForce, double curviness)

double calcValue (const SimTK::Vector &x) const override
Implement the generic OpenSim::Function interface. More...

double calcValue (double normFiberLength) const
Evaluates the fiber-force-length curve at a normalized fiber length of 'normFiberLength'. More...

double calcDerivative (double normFiberLength, int order) const
Calculates the derivative of the fiber-force-length multiplier with respect to the normalized fiber length. More...

double calcDerivative (const std::vector< int > &derivComponents, const SimTK::Vector &x) const override
If possible, use the simpler overload above. More...

double calcIntegral (double normFiberLength) const
Calculates the normalized area under the curve. More...

SimTK::Vec2 getCurveDomain () const
Returns a SimTK::Vec2 containing the lower (0th element) and upper (1st element) bounds on the domain of the curve. More...

void printMuscleCurveToCSVFile (const std::string &path)
Generates a .csv file with a name that matches the curve name (e.g., "bicepsfemoris_FiberForceLengthCurve.csv"). More...

void ensureCurveUpToDate ()

Property-related functions
const double & get_strain_at_zero_force () const
Get the value of the strain_at_zero_force property. More...

double & upd_strain_at_zero_force ()
Get a writable reference to the strain_at_zero_force property. More...

void set_strain_at_zero_force (const double &value)
Set the value of the strain_at_zero_force property. More...

const double & get_strain_at_one_norm_force () const
Get the value of the strain_at_one_norm_force property. More...

double & upd_strain_at_one_norm_force ()
Get a writable reference to the strain_at_one_norm_force property. More...

void set_strain_at_one_norm_force (const double &value)
Set the value of the strain_at_one_norm_force property. More...

const double & get_stiffness_at_low_force () const
Get the value of the stiffness_at_low_force property. More...

double & upd_stiffness_at_low_force ()
Get a writable reference to the stiffness_at_low_force property. More...

void set_stiffness_at_low_force (const double &value)
Set the value of the stiffness_at_low_force property. More...

const double & get_stiffness_at_one_norm_force () const
Get the value of the stiffness_at_one_norm_force property. More...

double & upd_stiffness_at_one_norm_force ()
Get a writable reference to the stiffness_at_one_norm_force property. More...

void set_stiffness_at_one_norm_force (const double &value)
Set the value of the stiffness_at_one_norm_force property. More...

const double & get_curviness () const
Get the value of the curviness property. More...

double & upd_curviness ()
Get a writable reference to the curviness property. More...

void set_curviness (const double &value)
Set the value of the curviness property. More...

Public Member Functions inherited from OpenSim::Function
Function ()

Function (const Function &aFunction)

virtual ~Function ()

virtual void init (Function *aFunction)

Functionoperator= (const Function &aFunction)

virtual int getArgumentSize () const
Get the number of components expected in the input vector. More...

virtual int getMaxDerivativeOrder () const
Get the maximum derivative order this Function object can calculate. More...

void assign (Object &aObject) override
This allows copy assignment in the Java GUI. More...

Public Member Functions inherited from OpenSim::Object
virtual ~Object ()
Virtual destructor for cleanup. More...

bool isEqualTo (const Object &aObject) const
Equality operator wrapper for use from languages not supporting operator overloading. More...

Objectoperator= (const Object &aObject)
Copy assignment copies he base class fields, including the properties. More...

virtual bool operator== (const Object &aObject) const
Determine if two objects are equal. More...

virtual bool operator< (const Object &aObject) const
Provide an ordering for objects so they can be put in sorted containers. More...

void setName (const std::string &name)
Set the name of the Object. More...

const std::string & getName () const
Get the name of this Object. More...

void setDescription (const std::string &description)
Set description, a one-liner summary. More...

const std::string & getDescription () const
Get description, a one-liner summary. More...

const std::string & getAuthors () const
Get Authors of this Object. More...

void setAuthors (const std::string &authors)
Set Authors of this object. More...

const std::string & getReferences () const
Get references or publications to cite if using this object. More...

void setReferences (const std::string &references)
Set references or publications to cite if using this object. More...

int getNumProperties () const
Determine how many properties are stored with this Object. More...

const AbstractPropertygetPropertyByIndex (int propertyIndex) const
Get a const reference to a property by its index number, returned as an AbstractProperty. More...

AbstractPropertyupdPropertyByIndex (int propertyIndex)
Get a writable reference to a property by its index number, returned as an AbstractProperty. More...

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. More...

const AbstractPropertygetPropertyByName (const std::string &name) const
Get a const reference to a property by its name, returned as an AbstractProperty. More...

AbstractPropertyupdPropertyByName (const std::string &name)
Get a writable reference to a property by its name, returned as an AbstractProperty. More...

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. More...

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. More...

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. More...

bool isObjectUpToDateWithProperties () const
Returns true if no property's value has changed since the last time setObjectIsUpToDateWithProperties() was called. More...

void readObjectFromXMLNodeOrFile (SimTK::Xml::Element &objectElement, int versionNumber)
We're given an XML element from which we are to populate this Object. More...

virtual void updateFromXMLNode (SimTK::Xml::Element &objectElement, int versionNumber)
Use this method to deserialize an object from a SimTK::Xml::Element. More...

void updateXMLNode (SimTK::Xml::Element &parent, const AbstractProperty *prop=nullptr) const
Serialize this object into the XML node that represents it. More...

bool getInlined () const
Inlined means an in-memory Object that is not associated with an XMLDocument. More...

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. More...

std::string getDocumentFileName () const
If there is a document associated with this object then return the file name maintained by the document. More...

int getDocumentFileVersion () const
If there is a document associated with this object then return its version number. More...

void setAllPropertiesUseDefault (bool aUseDefault)

bool print (const std::string &fileName) const
Write this Object into an XML file of the given name; conventionally the suffix to use is ".osim". More...

std::string dump () const
dump the XML representation of this Object into an std::string and return it. More...

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. More...

const std::string & toString () const
Wrapper to be used on Java side to display objects in tree; this returns just the object's name. More...

PropertySetgetPropertySet ()
OBSOLETE: Get a reference to the PropertySet maintained by the Object. More...

const PropertySetgetPropertySet () const

## Public Types

typedef FiberForceLengthCurve Self
This typedef might be useful within the member functions of this class. More...

typedef Function Super
Use this typedef to refer to the superclass of this class. More...

Public Types inherited from OpenSim::Function
typedef Function Self
This typedef might be useful within the member functions of this class. More...

typedef Object Super
Use this typedef to refer to the superclass of this class. More...

## Auto-generated functions

static FiberForceLengthCurvesafeDownCast (OpenSim::Object *obj)
For use in MATLAB and Python to access the concrete class. More...

static const std::string & getClassName ()
This returns "FiberForceLengthCurve". More...

void assign (Object &aObject) override
This allows copy assignment in the Java GUI. More...

FiberForceLengthCurveclone () const override
Create a new heap-allocated copy of the concrete object to which this Object refers. More...

const std::string & getConcreteClassName () const override
Returns the class name of the concrete Object-derived class of the actual object referenced by this Object, as a string. More...

Static Public Member Functions inherited from OpenSim::Function
static FunctionmakeFunctionOfType (Function *aFunction, const std::string &aNewTypeName)

static FunctionsafeDownCast (OpenSim::Object *obj)
For use in MATLAB and Python to access the concrete class. More...

static const std::string & getClassName ()
This returns "Function". More...

Static Public Member Functions inherited from OpenSim::Object
static void registerType (const Object &defaultObject)
Register an instance of a class; if the class is already registered it will be replaced. More...

static void renameType (const std::string &oldTypeName, const std::string &newTypeName)
Support versioning by associating the current Object type with an old name. More...

static const ObjectgetDefaultInstanceOfType (const std::string &concreteClassName)
Return a pointer to the default instance of the registered (concrete) Object whose class name is given, or NULL if the type is not registered. More...

template<class T >
static bool isObjectTypeDerivedFrom (const std::string &concreteClassName)
Return true if the given concrete object type represents a subclass of the template object type T, and thus could be referenced with a T*. More...

static ObjectnewInstanceOfType (const std::string &concreteClassName)
Create a new instance of the concrete Object type whose class name is given as concreteClassName. More...

static void getRegisteredTypenames (Array< std::string > &typeNames)
Retrieve all the typenames registered so far. More...

template<class T >
static void getRegisteredObjectsOfGivenType (ArrayPtrs< T > &rArray)
Return an array of pointers to the default instances of all registered (concrete) Object types that derive from a given Object-derived type that does not have to be concrete. More...

static bool PrintPropertyInfo (std::ostream &os, const std::string &classNameDotPropertyName, bool printFlagInfo=true)
Dump formatted property information to a given output stream, useful for creating a "help" facility for registered objects. More...

static bool PrintPropertyInfo (std::ostream &os, const std::string &className, const std::string &propertyName, bool printFlagInfo=true)
Same as the other signature but the class name and property name are provided as two separate strings. More...

static ObjectmakeObjectFromFile (const std::string &fileName)
Create an OpenSim object whose type is based on the tag at the root node of the XML file passed in. More...

static const std::string & getClassName ()
Return the name of this class as a string; i.e., "Object". More...

static void setSerializeAllDefaults (bool shouldSerializeDefaults)
Static function to control whether all registered objects and their properties are written to the defaults section of output files rather than only those values for which the default was explicitly overwritten when read in from an input file or set programmatically. More...

static bool getSerializeAllDefaults ()
Report the value of the "serialize all defaults" flag. More...

static bool isKindOf (const char *type)
Returns true if the passed-in string is "Object"; each Object-derived class defines a method of this name for its own class name. More...

static void setDebugLevel (int newLevel)
Set the amount of logging output. More...

static int getDebugLevel ()
Get the current setting of debug level. More...

static ObjectSafeCopy (const Object *aObject)
Use the clone() method to duplicate the given object unless the pointer is null in which case null is returned. More...

static void RegisterType (const Object &defaultObject)
OBSOLETE alternate name for registerType(). More...

static void RenameType (const std::string &oldName, const std::string &newName)
OBSOLETE alternate name for renameType(). More...

Static Public Attributes inherited from OpenSim::Object
static const std::string DEFAULT_NAME
Name used for default objects when they are serialized. More...

Protected Member Functions inherited from OpenSim::Function
void resetFunction ()
This should be called whenever this object has been modified. More...

Protected Member Functions inherited from OpenSim::Object
Object ()
The default constructor is only for use by constructors of derived types. More...

Object (const std::string &fileName, bool aUpdateFromXMLNode=true)
Constructor from a file, to be called from other constructors that take a file as input. More...

Object (const Object &source)
Copy constructor is invoked automatically by derived classes with default copy constructors; otherwise it must be invoked explicitly. More...

Object (SimTK::Xml::Element &aElement)
Construct the base class portion of an Object from a given Xml element that describes this Object. More...

template<class T >
PropertyIndex addProperty (const std::string &name, const std::string &comment, const T &value)
Define a new single-value property of known type T, with the given name, associated comment, and initial value. More...

template<class T >
PropertyIndex addOptionalProperty (const std::string &name, const std::string &comment)
Add an optional property, meaning it can contain either no value or a single value. More...

template<class T >
PropertyIndex addOptionalProperty (const std::string &name, const std::string &comment, const T &value)
Add an optional property, meaning it can contain either no value or a single value. More...

template<class T >
PropertyIndex addListProperty (const std::string &name, const std::string &comment, int minSize, int maxSize)
Define a new list-valued property of known type T, with the given name, associated comment, minimum (==0) and maximum (>0) allowable list lengths, and a zero-length initial value. More...

template<class T , template< class > class Container>
PropertyIndex addListProperty (const std::string &name, const std::string &comment, int minSize, int maxSize, const Container< T > &valueList)
Define a new list-valued property as above, but assigning an initial value via some templatized container class that supports size() and indexing. More...

PropertyIndex getPropertyIndex (const std::string &name) const
Look up a property by name and return its PropertyIndex if it is found. More...

template<class T >
PropertyIndex getPropertyIndex () const
Look up an unnamed property by the type of object it contains, and return its PropertyIndex if it is found. More...

template<class T >
void checkPropertyValueIsPositive (const Property< T > &p) const
Throw an exception if any of the property's values are not positive. More...

template<class T >
void checkPropertyValueIsInSet (const Property< T > &p, const std::set< T > &set) const
Throw an exception if any of the property's values are not in the provided set. More...

template<class T >
void checkPropertyValueIsInRangeOrSet (const Property< T > &p, const T &lower, const T &upper, const std::set< T > &set) const
Throw an exception if any of the property's values are neither in the provided range nor in the provided set. More...

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. More...

void clearObjectIsUpToDateWithProperties ()
For testing or debugging purposes, manually clear the "object is up to date with respect to properties" flag. More...

void makeObjectNamesConsistentWithProperties ()
Make sure the name of an object is consistent with its property type. More...

void updateFromXMLDocument ()
Use this method only if you're deserializing from a file and the object is at the top level; that is, primarily in constructors that take a file name as input. More...

void setDocument (XMLDocument *doc)
Unconditionally set the XMLDocument associated with this object. More...

const XMLDocumentgetDocument () const
Get a const pointer to the document (if any) associated with this object. More...

XMLDocumentupdDocument ()
Get a writable pointer to the document (if any) associated with this object. More...

Protected Attributes inherited from OpenSim::Function
SimTK::Function * _function

Protected Attributes inherited from OpenSim::Object
PropertySet _propertySet
OBSOLETE: Property_Deprecated set for serializable member variables of this and derived classes. More...

## Detailed Description

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'):

### Properties

• 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 Properties

• strainAtZeroForce
• strainAtOneNormForce

### Optional Properties

• stiffnessAtLowForce
• stiffnessAtOneNormForce
• curviness

### 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

// Make a fitted fiber-force-length curve.
fpeCurve1.setCurveStrains(0.0, 0.7);
double fpeVal1 = fpeCurve1.calcValue(0.1);
// Make a custom fiber-force-length curve by supplying all parameters.
FiberForceLengthCurve fpeCurve2(0.0, 0.7, 0.2, 2.86, 0.75);
double fpeVal2 = fpeCurve2.calcValue(0.02);
double dfpeVal2 = fpeCurve2.calcDerivative(0.02, 1);

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

• Thelen, D.G. (2003) Adjustment of muscle mechanics model parameters to simulate dynamic contractions in older adults. ASME Journal of Biomechanical Engineering 125:70–77.
• Winters, T.M., Takahashi, M., Lieber, R.L., and Ward, S. (2010) Whole muscle length-tension relationships are accurately modeled as scaled sarcomeres in rabbit hindlimb muscles. Journal of Biomechanics 44:109–115.

## ◆ Self

This typedef might be useful within the member functions of this class.

This is generated by the OpenSim_DECLARE_*_OBJECT macros.

## ◆ Super

Use this typedef to refer to the superclass of this class.

Avoid using the explicit type name of the superclass; this would introduce bugs if the superclass is changed.

This is generated by the OpenSim_DECLARE_*_OBJECT macros.

## ◆ FiberForceLengthCurve() [1/2]

 OpenSim::FiberForceLengthCurve::FiberForceLengthCurve ( )

The default constructor creates a fiber-force-length curve using the default property values and assigns a default name.

## ◆ FiberForceLengthCurve() [2/2]

 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.

See class documentation for the meaning of these parameters, each of which corresponds to a property.

## ◆ assign()

 void OpenSim::FiberForceLengthCurve::assign ( Object & aObject )
inlineoverride

This allows copy assignment in the Java GUI.

Exceptions
 Exception if the argument is not of type FiberForceLengthCurve.

## ◆ calcDerivative() [1/2]

 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.

Parameters
 normFiberLength The normalized length of the muscle fiber. order The order of the derivative. Only values of 0, 1, and 2 are acceptable.
Returns
The derivative of the fiber-force-length curve with respect to the normalized fiber length.

## ◆ calcDerivative() [2/2]

 double OpenSim::FiberForceLengthCurve::calcDerivative ( const std::vector< int > & derivComponents, const SimTK::Vector & x ) const
overridevirtual

If possible, use the simpler overload above.

Reimplemented from OpenSim::Function.

## ◆ calcIntegral()

 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.

Parameters
 normFiberLength The normalized length of the muscle fiber.
Returns
The normalized area under the curve, which corresponds to the normalized potential energy stored in the fiber. To calculate the potential energy stored in the fiber in units of Joules, multiply the returned quantity by normForce*normLength (where normForce is the number of Newtons represented by a normalized force of 1.0 and normLength is the number of meters represented by a normalized length of 1.0).

## ◆ calcValue() [1/2]

 double OpenSim::FiberForceLengthCurve::calcValue ( const SimTK::Vector & x ) const
inlineoverridevirtual

Implement the generic OpenSim::Function interface.

Reimplemented from OpenSim::Function.

## ◆ calcValue() [2/2]

 double OpenSim::FiberForceLengthCurve::calcValue ( double normFiberLength ) const

Evaluates the fiber-force-length curve at a normalized fiber length of 'normFiberLength'.

## ◆ clone()

 FiberForceLengthCurve* OpenSim::FiberForceLengthCurve::clone ( ) const
inlineoverridevirtual

Create a new heap-allocated copy of the concrete object to which this Object refers.

It is up to the caller to delete the returned object when no longer needed. Every concrete object deriving from Object implements this pure virtual method automatically, via the declaration macro it invokes (e.g., OpenSim_DECLARE_CONCRETE_OBJECT()). Note that the concrete class overrides modify the return type to be a pointer to the concrete object; that still overrides the base class method because the return type is covariant with (that is, derives from) Object.

Implements OpenSim::Function.

## ◆ ensureCurveUpToDate()

 void OpenSim::FiberForceLengthCurve::ensureCurveUpToDate ( )

## ◆ get_curviness()

 const double& OpenSim::FiberForceLengthCurve::get_curviness ( ) const
inline

Get the value of the curviness property.

## ◆ get_stiffness_at_low_force()

 const double& OpenSim::FiberForceLengthCurve::get_stiffness_at_low_force ( ) const
inline

Get the value of the stiffness_at_low_force property.

## ◆ get_stiffness_at_one_norm_force()

 const double& OpenSim::FiberForceLengthCurve::get_stiffness_at_one_norm_force ( ) const
inline

Get the value of the stiffness_at_one_norm_force property.

## ◆ get_strain_at_one_norm_force()

 const double& OpenSim::FiberForceLengthCurve::get_strain_at_one_norm_force ( ) const
inline

Get the value of the strain_at_one_norm_force property.

## ◆ get_strain_at_zero_force()

 const double& OpenSim::FiberForceLengthCurve::get_strain_at_zero_force ( ) const
inline

Get the value of the strain_at_zero_force property.

## ◆ getClassName()

 static const std::string& OpenSim::FiberForceLengthCurve::getClassName ( )
inlinestatic

This returns "FiberForceLengthCurve".

See getConcreteClassName() if you want the class name of the underlying concrete object instead.

This is generated by the OpenSim_DECLARE_*_OBJECT macros.

## ◆ getConcreteClassName()

 const std::string& OpenSim::FiberForceLengthCurve::getConcreteClassName ( ) const
inlineoverridevirtual

Returns the class name of the concrete Object-derived class of the actual object referenced by this Object, as a string.

This is the string that is used as the tag for this concrete object in an XML file. Every concrete class derived from Object automatically overrides this method via the declaration macro it uses. See getClassName() to get the class name of the referencing (possibly abstract) class rather than the concrete object.

getClassName()

Implements OpenSim::Function.

## ◆ getCurveDomain()

 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.

Returns
The minimum and maximum value of the domain, x, of the curve y(x). Within this range, y(x) is a curve; outside this range, the function y(x) is a C2-continuous linear extrapolation.

## ◆ getCurvinessInUse()

 double OpenSim::FiberForceLengthCurve::getCurvinessInUse ( ) const
Returns
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 in the class description. This property is set to 0.75 by default.

## ◆ getStiffnessAtLowForceInUse()

 double OpenSim::FiberForceLengthCurve::getStiffnessAtLowForceInUse ( ) const
Returns
The normalized stiffness (slope of the curve) when the fiber is just beginning to develop tensile force. This property is set to 0.125 by default.

## ◆ getStiffnessAtOneNormForceInUse()

 double OpenSim::FiberForceLengthCurve::getStiffnessAtOneNormForceInUse ( ) const
Returns
The normalized stiffness (slope of the curve) when the fiber develops a tension of 1 normalized unit of force. This property is set to 5.0 by default.

## ◆ getStrainAtOneNormForce()

 double OpenSim::FiberForceLengthCurve::getStrainAtOneNormForce ( ) const
Returns
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. This property is set to 0.6 by default.

## ◆ getStrainAtZeroForce()

 double OpenSim::FiberForceLengthCurve::getStrainAtZeroForce ( ) const
Returns
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. This property is set to 0 by default.

## ◆ isFittedCurveBeingUsed()

 bool OpenSim::FiberForceLengthCurve::isFittedCurveBeingUsed ( ) const
Returns
True if the optional properties are empty and the fitted curve is being used, false if the optional properties are filled and are being used to construct the curve.

## ◆ printMuscleCurveToCSVFile()

 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.

Parameters
 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);


## ◆ safeDownCast()

 static FiberForceLengthCurve* OpenSim::FiberForceLengthCurve::safeDownCast ( OpenSim::Object * obj )
inlinestatic

For use in MATLAB and Python to access the concrete class.

Example: cObj = FiberForceLengthCurve.safeDownCast(obj). This is equivalent to dynamic_cast<FiberForceLengthCurve*>(obj) in C++.

## ◆ set_curviness()

 void OpenSim::FiberForceLengthCurve::set_curviness ( const double & value )
inline

Set the value of the curviness property.

## ◆ set_stiffness_at_low_force()

 void OpenSim::FiberForceLengthCurve::set_stiffness_at_low_force ( const double & value )
inline

Set the value of the stiffness_at_low_force property.

## ◆ set_stiffness_at_one_norm_force()

 void OpenSim::FiberForceLengthCurve::set_stiffness_at_one_norm_force ( const double & value )
inline

Set the value of the stiffness_at_one_norm_force property.

## ◆ set_strain_at_one_norm_force()

 void OpenSim::FiberForceLengthCurve::set_strain_at_one_norm_force ( const double & value )
inline

Set the value of the strain_at_one_norm_force property.

## ◆ set_strain_at_zero_force()

 void OpenSim::FiberForceLengthCurve::set_strain_at_zero_force ( const double & value )
inline

Set the value of the strain_at_zero_force property.

## ◆ setCurveStrains()

 void OpenSim::FiberForceLengthCurve::setCurveStrains ( double aStrainAtZeroForce, double aStrainAtOneNormForce )
Parameters
 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


## ◆ setOptionalProperties()

 void OpenSim::FiberForceLengthCurve::setOptionalProperties ( double stiffnessAtLowForce, double stiffnessAtOneNormForce, double curviness )
Parameters
 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


## ◆ upd_curviness()

 double& OpenSim::FiberForceLengthCurve::upd_curviness ( )
inline

Get a writable reference to the curviness property.

## ◆ upd_stiffness_at_low_force()

 double& OpenSim::FiberForceLengthCurve::upd_stiffness_at_low_force ( )
inline

Get a writable reference to the stiffness_at_low_force property.

## ◆ upd_stiffness_at_one_norm_force()

 double& OpenSim::FiberForceLengthCurve::upd_stiffness_at_one_norm_force ( )
inline

Get a writable reference to the stiffness_at_one_norm_force property.

## ◆ upd_strain_at_one_norm_force()

 double& OpenSim::FiberForceLengthCurve::upd_strain_at_one_norm_force ( )
inline

Get a writable reference to the strain_at_one_norm_force property.

## ◆ upd_strain_at_zero_force()

 double& OpenSim::FiberForceLengthCurve::upd_strain_at_zero_force ( )
inline

Get a writable reference to the strain_at_zero_force property.

## ◆ curviness

 double OpenSim::FiberForceLengthCurve::curviness

"Fiber curve bend, from linear (0) to maximum bend (1)"

This property appears in XML files under the tag <curviness>. This property was generated with the OpenSim_DECLARE_OPTIONAL_PROPERTY macro; see Property to learn about the property system.

get_curviness(), upd_curviness(), set_curviness()

## ◆ stiffness_at_low_force

 double OpenSim::FiberForceLengthCurve::stiffness_at_low_force

"Fiber stiffness at the end of the low-force region"

This property appears in XML files under the tag <stiffness_at_low_force>. This property was generated with the OpenSim_DECLARE_OPTIONAL_PROPERTY macro; see Property to learn about the property system.

get_stiffness_at_low_force(), upd_stiffness_at_low_force(), set_stiffness_at_low_force()

## ◆ stiffness_at_one_norm_force

 double OpenSim::FiberForceLengthCurve::stiffness_at_one_norm_force

"Fiber stiffness at a tension of 1 normalized force"

This property appears in XML files under the tag <stiffness_at_one_norm_force>. This property was generated with the OpenSim_DECLARE_OPTIONAL_PROPERTY macro; see Property to learn about the property system.

get_stiffness_at_one_norm_force(), upd_stiffness_at_one_norm_force(), set_stiffness_at_one_norm_force()

## ◆ strain_at_one_norm_force

 double OpenSim::FiberForceLengthCurve::strain_at_one_norm_force

"Fiber strain at a tension of 1 normalized force"

This property appears in XML files under the tag <strain_at_one_norm_force>. This property was generated with the OpenSim_DECLARE_PROPERTY macro; see Property to learn about the property system.

get_strain_at_one_norm_force(), upd_strain_at_one_norm_force(), set_strain_at_one_norm_force()

## ◆ strain_at_zero_force

 double OpenSim::FiberForceLengthCurve::strain_at_zero_force

"Fiber strain at zero force"

This property appears in XML files under the tag <strain_at_zero_force>. This property was generated with the OpenSim_DECLARE_PROPERTY macro; see Property to learn about the property system.