MATLAB File Help: corrint View code for corrint WFDB Contents
corrint
```

function varargout=corrint(varargin)

[y1,y2,y3]=corrint(x,embeddedDim,timeLag,timeStep,distanceThreshold,neighboorSize,estimationMode,findScaling)

Correlation integral analysis of a time series. Based on:

[1] Kaplan, Daniel, and Leon Glass. Understanding nonlinear dynamics. Vol. 19. Springer, 1995.
[2] Kantz, Holger, and Thomas Schreiber. Nonlinear time series analysis. Cambridge university press, 2004.

Required input parameter:
x
Nx1 matrix (doubles) of time series to be analyzed.

Optional Parameters are:

embeddedDim
1x1 Integer specifying the embedded dimension size to use (default
=2).

timeLag
1x1 Integer specifying the minimum time lag distance (in samples) of the point to
be estimated. Default is 2. If timeLag=-1 the timeLag is estimated
from the first zero-crossing point of the autocorrelation of x.

timeStep
1x1 Integer specifying time lag distance (in samples) within
each point used in the embeddedDimm vector. For example, if embeddedDim
is 3 and timeStep =2, then the embedded dimension vector will consists of
3 samples separated by 2 samples each, covering a window of size of 7 samples.

distanceThreshold
1x1 double specifying the distance threshold between embedded
points. The points who's distance is less than distanceThreshold are considered in
the same neighborhood and used for either prediction, recurrence, or the
estimation of the embedded dimension.

neighboorSize
1x1 Integer specifying the number of neighbors to be used for
prediction and smoothing (see 'estimationMode' parameter).

estimationMode
String specifying what analysis type to be done in the time series.
Options are:
'recurrence'  -Calculates recurrence data to be used
in for recurrence plots (default).
'dimension'   -Generates statistics for the estimation of the correlation dimension
of the time series and it's scaling
regions.
'prediction'  -Predicts second half of the time
series using the first half as a model
and neighboorSize nearest points.
'smooth'      -Predicts all point of the times
series using all other points as a
model and neighboorSize nearest
points.

findScaling
1x1 Boolean flag to be passed when using 'dimension' mode. If set to
true, the scaling region will be searched automatically, using
r1=std(x)/4 and r2 -> C(r1)/C(r2) ~ 5. Default value is false.

The output returned by CORRINT is dependent on the 'estimationMode'
parameter, so that the description of the output below is broken down into the
different possible options for the 'estimationMode' parameter.

Output Parameters - 'recurrence' mode
y1
Lx1 Vector of integers for state i.
y2
Lx1 Vector of integers for state state j that is a neighbor of state i (first column).

Output Parameters - 'dimension' mode
y1
Lx1 Vector of doubles of log(distanceThreshold).
y2
Lx1 Vector of doubles for log(neighborhood size) given the distanceThreshold used in column 1.
y3
1x1 double. Optional, estimated slope of y1 and y2

Output Parameters - 'prediction' mode
y1
Lx1 Vector of doubles of estimated second half of the time series.
y2
Lx1 Vector of doubles for original second half of the time series.
y3
1x1 double. Optional, variance of the prediction error divided by variance of the second half of the time series.

Output Parameters - 'smooth' mode
y1
Lx1 Vector of doubles of smoothed the time series.
y2
Lx1 Vector of doubles for original time series.
y3
1x1 double. Optional, variance of the prediction error divided by variance of the time series.

%%% Beging Example %%%

N=500; %Number of points for each process
model_names={'linearModel','nonlinearModel'};

%Linear Auto Regressive model with measurement noise
linearModel=zeros(N,1);
x=77;
linearModel(1)=x;
for n=2:N
x=4 + 0.95*x;
linearModel(n)= x + randn(1)*2;
end

%Non-linear model of dimension ~ 3.9
nonlinearModel=zeros(N,1);
x=0.2;y=0.2;z=0.2;v=0.2;model_five(1)=x;
for n=2:N
m=0.4 - 6/(1+ x^2 + y^2);
xold=x;yold=y;zold=z;vold=v;
x= 1 + 0.7*(xold*cos(m)-yold*sin(m)) + 0.2*zold;
y=0.7*(xold*sin(m) + yold*cos(m));
z=1.4 + 0.3*vold - zold^2;
v=zold;
nonlinearModel(n)= x + 0.3*z + randn(1)*0.05;
end

%Plot time series
figure(1)
for i=1:2
subplot(2,1,i)
eval(['plot(' model_names{i} ');legend(''' model_names{i} ''')'])
title('Time Plot');xlabel('time')
end

%Plot cross correlation
figure(2)
for i=1:2
subplot(2,1,i)
eval(['x=' model_names{i} ';'])
R=xcorr(x-mean(x),'coeff');
plot(R(round(N):end))
eval(['legend(''' model_names{i} ''')'])
title('Autocorelation'); xlabel('lag')
end

%Plot Phase Plots
figure(3)
for i=1:2
subplot(2,1,i)
eval(['x=' model_names{i} ';'])
scatter(x(1:end-1),x(2:end))
eval(['legend(''' model_names{i} ''')'])
title('Phase Plot');xlabel('x(t)');ylabel('x(t+1)')
end

%Plot prediction errors vs surrogate
timeLag=1;
timeStep=1;
distanceThreshold=[];
embeddedDim=4;
estimationMode='smooth';
figure(4)
K=[1:20 25 30 50 70 100];
D=length(K);
surrN=10;
for i=1:2
eval(['x=' model_names{i} ';'])
err=zeros(D,1)+NaN;
surr_data=zeros(D,surrN);
SURR=surrogate(x,surrN);
for d=1:D;
neighboorSize=K(d);
[y1,y2,y3]=corrint(x,embeddedDim,timeLag,timeStep,distanceThreshold,neighboorSize,estimationMode);
err(d)=y3;
for s=1:surrN
[y1,y2,y3]=corrint(SURR(:,s),embeddedDim,timeLag,timeStep,distanceThreshold,neighboorSize,estimationMode);
surr_data(d,s)=y3;
end
end
subplot(2,1,i)
plot(K,err,'o-');hold on
errorbar(K,mean(surr_data,2),var(surr_data,[],2)./sqrt(10),'r')
eval(['legend(''' model_names{i} ''',''surrogate'')'])
xlabel('Embedded Dimension')
ylabel('err/var')

end

%%% End Example %%%

Written by Ikaro Silva, 20134