distFrechet: ~ Function: Frechet distance ~
In kmlShape: K-Means for Longitudinal Data using Shape-Respecting Distance

Description Usage Arguments Details Value Author References See Also Examples

Compute Frechet distance between two trajectories.

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distFrechet(Px,Py,Qx, Qy, timeScale=0.1, FrechetSumOrMax = "sum")
distFrechetR(Px,Py,Qx, Qy, timeScale=0.1, FrechetSumOrMax = "sum")
distFrechetRec(Px,Py,Qx, Qy, timeScale=0.1, FrechetSumOrMax = "sum")

`Px`	[vector(numeric)] Times (abscisse) of the first trajectories.
`Py`	[vector(numeric)] Values of the first trajectories.
`Qx`	[vector(numeric)] Times of the second trajectories.
`Qy`	[vector(numeric)] Values of the second trajectories.
`timeScale`	[`numeric`]: allow to modify the time scale, increasing or decreasing the cost of the horizontal shift. If timeScale is very big, then the Frechet's distance is equal to the euclidienne distance. If timeScale is very small, then it is equal to the Dynamic Time Warping.
`FrechetSumOrMax`	[`character`]: The Frechet's distance can be define using the 'sum' function or the 'max' function. This option let the user to chose one or the other.

Given two curve P and Q, Frechet distance between P and Q is define as inf_{a,b} max_{t} d(P(a(t)),Q(b(t))). It's computation is a NP-complex problem. When P and Q are trajectories (discrete curve), the problem is polynomial.

The Frechet distance can also be define using a sum instead of a max: inf_{a,b} sum_{t} d(P(a(t)),Q(b(t)))

The function distFrechet is C compiled, the function distFrechetR is in R, the function distFrechetRec is in recursive (the slowest) in R.

A numeric value.

Christophe Genolini
1. UMR U1027, INSERM, Universit<e9> Paul Sabatier / Toulouse III / France
2. CeRSM, EA 2931, UFR STAPS, Universit<e9> de Paris Ouest-Nanterre-La D<e9>fense / Nanterre / France

[1] Thomas Eiter & Heikki Mannila:
"Computing Discrete Fr<b4>echet Distance"

[2] C. Genolini and B. Falissard
"KmL: k-means for longitudinal data"
Computational Statistics, vol 25(2), pp 317-328, 2010

[3] C. Genolini and B. Falissard
"KmL: A package to cluster longitudinal data"
Computer Methods and Programs in Biomedicine, 104, pp e112-121, 2011

distTraj

   Px <- 1:20
   Py <- dnorm(1:20,12,2)
   Qx <- 1:20
   Qy <- dnorm(1:20,8,2)

   ### Function from Eiter and Mannila compiled in C
   system.time(cat("\n",distFrechet(Px,Py,Qx,Qy)))

   ### Same thing in R
   system.time(cat("\n",distFrechetR(Px,Py,Qx,Qy)))

   ### Frechet using sum instead of max.
   distFrechet(Px,Py,Qx,Qy,FrechetSumOrMax="sum")

Loading required package: class
Loading required package: longitudinalData
Loading required package: clv
Loading required package: cluster
Loading required package: rgl
Loading required package: misc3d
Loading required package: kml
Loading required package: lattice

Attaching package: 'kmlShape'

The following object is masked from 'package:longitudinalData':

    distFrechet

Warning messages:
1: In rgl.init(initValue, onlyNULL) : RGL: unable to open X11 display
2: 'rgl_init' failed, running with rgl.useNULL = TRUE 
3: .onUnload failed in unloadNamespace() for 'rgl', details:
  call: fun(...)
  error: object 'rgl_quit' not found 

 1.344959   user  system elapsed 
  0.001   0.000   0.000 

 1.344959   user  system elapsed 
  0.016   0.000   0.016 
[1] 1.344959