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org.apache.jmeter.visualizers
Class Spline3  

java.lang.Object
  org.apache.jmeter.visualizers.Spline3

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public class Spline3

extends java.lang.Object

This class implements the representation of an interpolated Spline curve.

The curve described by such an object interpolates an arbitrary number of fixed points called nodes. The distance between two nodes should currently be constant. This is about to change in a later version but it can last a while as it's not really needed. Nevertheless, if you need the feature, just write me a note and I'll write it asap.

The interpolated Spline curve can't be described by an polynomial analytic equation, the degree of which would be as high as the number of nodes, which would cause extreme oscillations of the curve on the edges.

The solution is to split the curve accross a lot of little intervals : an interval starts at one node and ends at the next one. Then, the interpolation is done on each interval, according to the following conditions :

1. the interpolated curve is degree 3 : it's a cubic curve ;
2. the interpolated curve contains the two points delimiting the interval. This condition obviously implies the curve is continuous ;
3. the interpolated curve has a smooth slope : the curvature has to be the same on the left and the right sides of each node ;
4. the curvature of the global curve is 0 at both edges.

Every part of the global curve is represented by a cubic (degree-3) polynomial, the coefficients of which have to be computed in order to meet the above conditions.

This leads to a n-unknow n-equation system to resolve. One can resolve an equation system by several manners ; this class uses the Jacobi iterative method, particularly well adapted to this situation, as the diagonal of the system matrix is strong compared to the other elements. This implies the algorithm always converges ! This is not the case of the Gauss-Seidel algorithm, which is quite faster (it uses intermediate results of each iteration to speed up the convergence) but it doesn't converge in all the cases or it converges to a wrong value. This is not acceptable and that's why the Jacobi method is safer. Anyway, the gain of speed is about a factor of 3 but, for a 100x100 system, it means 10 ms instead of 30 ms, which is a pretty good reason not to explore the question any further :)

Here is a little piece of code showing how to use this class :

 // ... float[] nodes = {3F, 2F, 4F, 1F, 2.5F, 5F, 3F}; Spline3 curve =
 new Spline3(nodes); // ... public void paint(Graphics g) { int[] plot =
 curve.getPlots(); for (int i = 1; i < n; i++) { g.drawLine(i - 1, plot[i -
 1], i, plot[i]); } } // ...
 
 

Have fun with it !
Any comments, feedback, bug reports or suggestions will be appreciated.

Version:

$Revison$ updated $Date: 2005/07/12 20:50:29 $

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Field Summary
protected  float[][]	_A
protected  float[]	_B
protected  float[][]	_coefficients
protected  int	_m
protected  int	_maxIterations
protected  float	_minPrecision
protected  int	_n
protected  float[]	_r
protected  float[]	_rS
protected static int	DEFAULT_MAX_ITERATIONS
protected static float	DEFAULT_PRECISION
private static Logger	log

 

Constructor Summary

Spline3(float[] r)           Creates a new Spline curve by calculating the coefficients of each part of the curve, i.e.

 

Method Summary
protected  boolean	converge()           Test if the Jacobi resolution of the equation system converges.
void	debugCheck()           Manual check of the curve at the interpolated points.
int	getDefaultMaxIterations()
float	getDefaultPrecision()
int	getMaxIterations()
int[]	getPlots(int width, int height)           Computes drawable plots from the curve for a given draw space.
float	getPrecision()
protected  void	interpolation()           Computes the coefficients of the Spline interpolated curve, on each interval.
protected  void	jacobi()           Resolves the equation system by a Jacobi algorithm.
protected  float	precision(float[] oldX, float[] newX)           Computes the current precision reached.
void	setMaxIterations(int iterations)
void	setPrecision(float precision)
void	setToDefaultMaxIterations()
void	setToDefaultPrecision()
float	value(float t)           Computes a (vertical) Y-axis value of the global curve.

 

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Field Detail

log

private static transient Logger log

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_coefficients

protected float[][] _coefficients

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_A

protected float[][] _A

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_B

protected float[] _B

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_r

protected float[] _r

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_rS

protected float[] _rS

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_m

protected int _m

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_n

protected int _n

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DEFAULT_PRECISION

protected static final float DEFAULT_PRECISION

See Also:

Constant Field Values

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DEFAULT_MAX_ITERATIONS

protected static final int DEFAULT_MAX_ITERATIONS

See Also:

Constant Field Values

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_minPrecision

protected float _minPrecision

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_maxIterations

protected int _maxIterations

Constructor Detail

Spline3

public Spline3(float[] r)

Creates a new Spline curve by calculating the coefficients of each part of the curve, i.e. by resolving the equation system implied by the interpolation condition on every interval.

Method Detail

interpolation

protected void interpolation()

Computes the coefficients of the Spline interpolated curve, on each interval. The matrix system to resolve is AX=B

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jacobi

protected void jacobi()

Resolves the equation system by a Jacobi algorithm. The use of the slower Jacobi algorithm instead of Gauss-Seidel is choosen here because Jacobi is assured of to be convergent for this particular equation system, as the system matrix has a strong diagonal.

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converge

protected boolean converge()

Test if the Jacobi resolution of the equation system converges. It's OK if A has a strong diagonal.

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precision

protected float precision(float[] oldX,
                          float[] newX)

Computes the current precision reached.

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value

public float value(float t)

Computes a (vertical) Y-axis value of the global curve.

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debugCheck

public void debugCheck()

Manual check of the curve at the interpolated points.

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getPlots

public int[] getPlots(int width,
                      int height)

Computes drawable plots from the curve for a given draw space. The values returned are drawable vertically and from the bottom of a Panel.

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setPrecision

public void setPrecision(float precision)

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getPrecision

public float getPrecision()

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setToDefaultPrecision

public void setToDefaultPrecision()

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getDefaultPrecision

public float getDefaultPrecision()

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setMaxIterations

public void setMaxIterations(int iterations)

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getMaxIterations

public int getMaxIterations()

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setToDefaultMaxIterations

public void setToDefaultMaxIterations()

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getDefaultMaxIterations

public int getDefaultMaxIterations()

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> org >> apache >> jmeter >> [ visualizers overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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