changepoint (version 0.3)

multiple.reg.norm: Multiple Changes in Regression - Normal Errors

Description

Calculates the optimal positioning and number of changepoints for regression data with zero-mean Normal errors using the user specified method.

Usage

multiple.reg.norm(data,mul.method="PELT",penalty="SIC",value=0,Q=5,class=TRUE,param.estimates=TRUE)

Arguments

data

A matrix or 3-d array containing the data within which you wish to find a changepoint. If data is a 3-d array, each first dimension is considered a separate dataset. Within each dataset the first column is considered the response and the further columns

mul.method

Choice of "PELT", "SegNeigh" or "BinSeg".

penalty

Choice of "None", "SIC", "BIC", "AIC", "Hannan-Quinn", "Asymptotic" and "Manual" penalties. If Manual is specified, the manual penalty is contained in the value parameter. If Asymptotic is specified, the theoretical type I error is contained in the value

value

The theoretical type I error e.g.0.05 when using the Asymptotic penalty. The value of the penalty when using the Manual penalty option. This can be a numeric value or text giving the formula to use. Available variables are, n=length of original data, n

Q

The maximum number of changepoints to search for using the "BinSeg" method. The maximum number of segments (number of changepoints + 1) to search for using the "SegNeigh" method.

class

Logical. If TRUE then an object of class cpt is returned.

param.estimates

Logical. If TRUE and class=TRUE then parameter estimates are returned. If FALSE or class=FALSE no parameter estimates are returned.

Value

• If class=TRUE then an object of S4 class "cpt" is returned. The slot cpts contains the changepoints that are solely returned if class=FALSE. The structure of cpts is as follows. If data is a matrix (single dataset) then a vector/list is returned depending on the value of mul.method. If data is an array (multiple datasets) then a list is returned where each element in the list is either a vector or list depending on the value of mul.method.

  If mul.method is PELT then a vector is returned:

• cpt
  Vector containing the changepoint locations for the penalty supplied. This always ends with n.
• If mul.method is SegNeigh then a list is returned with elements:
• cps
  Matrix containing the changepoint positions for 1,...,Q changepoints.
• op.cpts
  The optimal changepoint locations for the penalty supplied.
• like
  Value of the -2*log(likelihood ratio) + penalty for the optimal number of changepoints selected.
• If mul.method is BinSeg then a list is returned with elements:
• cps
  2xQ Matrix containing the changepoint positions on the first row and the test statistic on the second row.
• op.cpts
  The optimal changepoint locations for the penalty supplied.
• pen
  Penalty used to find the optimal number of changepoints.

Details

This function is used to find multiple changes in regression for data that is assumed to have zero-mean normally distributed errors. The changes are found using the method supplied which can be exact (PELT or SegNeigh) or approximate (BinSeg).

References

Change in regression: Chen, J. and Gupta, A. K. (2000) Parametric statistical change point analysis, Birkhauser

PELT Algorithm: Killick, R. and Fearnhead, P. and Eckley, I.A. (2011) An exact linear time search algorithm for multiple changepoint detection, Submitted

Binary Segmentation: Scott, A. J. and Knott, M. (1974) A Cluster Analysis Method for Grouping Means in the Analysis of Variance, Biometrics 30(3), 507--512

Segment Neighbourhoods: Auger, I. E. And Lawrence, C. E. (1989) Algorithms for the Optimal Identification of Segment Neighborhoods, Bulletin of Mathematical Biology 51(1), 39--54

See Also

multiple.mean.norm,multiple.var.norm,multiple.meanvar.norm,cpt.reg,PELT.reg.norm,binseg.reg.norm,single.reg.norm,segneigh.reg.norm,cpt

Examples

# Example of multiple changes in regression at 100,250 in simulated data with zero-mean normal errors
set.seed(1)
x=1:400
y=c(0.01*x[1:100],3.5-0.02*x[101:250],-15+0.05*x[251:400])
ynoise=y+rnorm(400,0,0.2)
yx=cbind(ynoise,1,x)
multiple.reg.norm(yx,mul.method="BinSeg",penalty="Manual",value="4*log(n)",Q=5,class=FALSE) # returns optimal number of changepoints is 2, locations are 100,250.

# Example multiple datasets where the first has multiple changes in regression and the second has no change in regression
set.seed(1)
x1=1:400
y1=c(0.01*x1[1:100],3.5-0.02*x1[101:250],-15+0.05*x1[251:400])
ynoise1=y1+rnorm(400,0,0.2)
yx1=cbind(ynoise1,1,x1)

x2=1:400
y2=0.01*x2
ynoise2=y2+rnorm(400,0,0.2)
yx2=cbind(ynoise2,1,x2)

data=array(0,dim=c(2,400,3))
data[1,,]=yx1; data[2,,]=yx2

multiple.reg.norm(data,mul.method="SegNeigh",penalty="Asymptotic",value=0.01,Q=5,class=FALSE) # returns list that has two elements, the first has 2 changes in regression at 100,250 and the second has no changes in regression
ans=multiple.reg.norm(data,mul.method="PELT",penalty="Asymptotic",value=0.01) 
cpts(ans[[1]]) # same results as for the SegNeigh method.
cpts(ans[[2]]) # same results as for the SegNeigh method.