RatioFunction Class Reference

Represents a function computing a ratio of two values. More...

Inheritance diagram for RatioFunction:

Collaboration diagram for RatioFunction:

Public Member Functions
	RatioFunction ()
	Constructs a new ratio function.
	RatioFunction (double zeroOverZero)
	Constructs a new ratio function that returns zeroOverZero for the special case of \(0/0\). More...
double	getZeroOverZeroValue ()
	Returns the value returned by evaluate in the case where the \(0/0\) function is calculated. More...
void	setZeroOverZeroValue (double zeroOverZero)
	Sets the value returned by evaluate for the undefined function \(0/0\) to zeroOverZero. More...
int	getDimension ()
	Returns \(d\), the dimension of the function computed by this implementation. More...
double	evaluate (double... x)
	Computes the function \(g(\mathbf{x})\) for the vector x. More...
double	evaluateGradient (int i, double... x)
	Computes \(\partial g(\mathbf{x})/\partial x_i\), the derivative of \(g(\mathbf{x})\) with respect to \(x_i\). More...

Detailed Description

Represents a function computing a ratio of two values.

Constructor & Destructor Documentation

RatioFunction()

RatioFunction

(

double

zeroOverZero

)

Constructs a new ratio function that returns zeroOverZero for the special case of \(0/0\).

See the getZeroOverZeroValue method for more information. The default value of zeroOverZero is Double.NaN.

Parameters

zeroOverZero

the value for \(0/0\).

Member Function Documentation

evaluate()

double evaluate

(

double...

x

)

Computes the function \(g(\mathbf{x})\) for the vector x.

The length of the given array must correspond to the dimension of this function. The method must compute and return the result of the function without modifying the elements in x since the array can be reused for further computation.

Parameters

x	a vector \(\mathbf{x}\).

Returns

the value of \(g(\mathbf{x})\).

Exceptions

NullPointerException	if x is null.
IllegalArgumentException	if x.length does not correspond to the dimension of this function.

Implements MultivariateFunction.

evaluateGradient()

double evaluateGradient	(	int	i,
		double...	x
	)

Computes \(\partial g(\mathbf{x})/\partial x_i\), the derivative of \(g(\mathbf{x})\) with respect to \(x_i\).

The length of the given array must correspond to the dimension of this function. The method must compute and return the result of the derivative without modifying the elements in x since the array can be reused for further computations, e.g., the gradient \(\nabla g(\mathbf{x})\).

Parameters

i	the variable to derive with respect to.
x	a vector \(\mathbf{x}\).

Returns

the value of the partial derivative.

Exceptions

NullPointerException	if x is null.
IllegalArgumentException	if x.length does not correspond to the dimension of this function.
IndexOutOfBoundsException	if i is negative or greater than or equal to the dimension of this function.

Implements MultivariateFunction.

getDimension()

int getDimension

(

)

Returns \(d\), the dimension of the function computed by this implementation.

If the dimension is not fixed, this method must return a negative value.

Returns

the dimension.

Implements MultivariateFunction.

getZeroOverZeroValue()

double getZeroOverZeroValue

(

)

Returns the value returned by evaluate in the case where the \(0/0\) function is calculated.

The default value for \(0/0\) is Double.NaN.

Generally, \(0/0\) is undefined, and therefore associated with the Double.NaN constant, meaning not-a-number. However, in certain applications, it can be defined differently to accomodate some special cases. For exemple, in a queueing system, if there are no arrivals, no customers are served, lost, queued, etc. As a result, many performance measures of interest turn out to be \(0/0\). Specifically, the loss probability, i.e., the ratio of lost customers over the number of arrivals, should be 0 if there is no arrival; in this case, \(0/0\) means 0. On the other hand, the service level, i.e., the fraction of customers waiting less than a fixed threshold, could be fixed to 1 if there is no arrival.

Returns

the value for \(0/0\).

setZeroOverZeroValue()

void setZeroOverZeroValue

(

double

zeroOverZero

)

Sets the value returned by evaluate for the undefined function \(0/0\) to zeroOverZero.

See getZeroOverZeroValue for more information.

Parameters

zeroOverZero

the new value for \(0/0\).

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The documentation for this class was generated from the following file:

• RatioFunction.java