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### Highlights from error_ellipse

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# error_ellipse

### AJ Johnson (view profile)

01 Apr 2004 (Updated )

Plot an error ellipse depicting confidence interval given a covariance matrix.

File Information
Description

% ERROR_ELLIPSE - plot an error ellipse, or ellipsoid, defining
% confidence region
% ERROR_ELLIPSE(C22) - Given a 2x2 covariance matrix, plot the
% associated error ellipse, at the origin. It returns a graphics handle
% of the ellipse that was drawn.
%
% ERROR_ELLIPSE(C33) - Given a 3x3 covariance matrix, plot the
% associated error ellipsoid, at the origin, as well as its projections
% onto the three axes. Returns a vector of 4 graphics handles, for the
% three ellipses (in the X-Y, Y-Z, and Z-X planes, respectively) and for
% the ellipsoid.
%
% ERROR_ELLIPSE(C,MU) - Plot the ellipse, or ellipsoid, centered at % MU, a vector whose length should match that of C (which is 2x2
% or 3x3).
%
% ERROR_ELLIPSE(...,'Property1',Value1,'Name2',Value2,...) sets
% the values of specified properties, including:
% 'C' - Alternate method of specifying the covariance matrix
% 'mu' - Alternate method of specifying the ellipse (-oid) center
% 'conf' - A value betwen 0 and 1 specifying the confidence interval.
% the default is 0.5 which is the 50% error ellipse.
% 'scale' - Allow the plot the be scaled to difference units.
% 'style' - A plotting style used to format ellipses.
% 'clip' - specifies a clipping radius. Portions of the ellipse, -oid,
% outside the radius will not be shown.
%
% NOTES: C must be positive definite for this function to work
% properly.

Acknowledgements

This file inspired Gaussian Mixture Probability Hypothesis Density Filter (Gm Phd).

MATLAB release MATLAB 6.1 (R12.1)
MATLAB Search Path
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23 Jul 2015 Ahmed Fasih

### Ahmed Fasih (view profile)

Thanks AJ! Delicious BSD license :)

23 Jul 2015 Ahmed Fasih

### Ahmed Fasih (view profile)

What's the license on this submission, anyone know?

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04 Jun 2014 Jonathan Currie

### Jonathan Currie (view profile)

Should the second argument to qchisq not be the degrees of freedom, rather than the number of parameters?

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11 Dec 2013 Peter Farkas

### Peter Farkas (view profile)

This was excellent for learning about Kalman filters.

14 Aug 2013 Serena

### Serena (view profile)

Thank you,it was useful!
I have a question about the k value since I'm not familiar with statistics: why do you get it from a k square distribution and not from a normal distribution?

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11 Jun 2013 Christian

### Christian (view profile)

08 Feb 2013 Charles Nelatury

### Charles Nelatury (view profile)

02 May 2012 Burcu

### Burcu (view profile)

Really very helpful. But did not understand how to calculate k value from conf "k = sqrt(qchisq(conf,r))" Does anybody know how this relation holds? Thanks..

Thanks. Saved a lot of my time.

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26 Oct 2011 Takuma

### Takuma (view profile)

29 Sep 2011 Anthony

### Anthony (view profile)

Very helpful and easy to use.

09 Apr 2011 gunes bay1r

### gunes bay1r (view profile)

thanks for conf. interval comment phil fox

21 Mar 2011 Claus

### Claus (view profile)

Ooops, there's an obvious mistake in my area/volume calculation from above. I forgot to factor in the quantile for the desired percentile, i.e., you have to multiply the area/volume with the quantile of the desired confidence interval (conf). You can use the embedded functions from error_ellipse to calculate Pconf (for the default of conf=0.5, Pconf(2D)=1.1774/Pconf(3D)=1.5382). The formular for area (volume accordingly) should read:
area=prod(sqrt(eig(C)))*pi*Pconf

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18 Mar 2011 Claus

### Claus (view profile)

@Jenn Risk & @me: Finally got a solution for area/volume. It's all based on the eigenvalues of the CovMatrix (the prerequisite for error_ellipse).
Area (2D): area=prod(sqrt(eig(C)))*pi
Volume (3D): volume=prod(sqrt(eig(C)))*4/3*pi

Hope that helps. Cheers!

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17 Mar 2011 Claus

### Claus (view profile)

Worked just great for me and saved a LOT of time writing my own code. Thanks!

I'm currently working on a area/volume calculation. @Ahmed Fasih: det(covMatrix) may definately be used as a measure, however, it's not the actual area/volume.

27 Dec 2010 Zohar Bar-Yehuda

### Zohar Bar-Yehuda (view profile)

01 Sep 2010 Ahmed Fasih

### Ahmed Fasih (view profile)

Jenn Risk: just use det(CovMatrix) for area/volume.

M ChC, Volkan Ozturk:
figure; handle(1)=error_ellipse(A); hold on; handle(2)=error_ellipse(B); handle(3)=error_ellipse(C); set(handle(2), 'color','r', 'linestyle',':'); set(handle(3), 'color','k', 'linestyle','--');

19 Aug 2010 Marcel

### Marcel (view profile)

Perfect piece of code! I am using it alot. Had to change the API though to make it a bit more flexible in terms of plot properties (e.g. passing it a parent axes handle).

22 Jun 2010 Ipsita

### Ipsita (view profile)

??? function h = error_ellipse(varargin)
|
Error: Function definitions are not permitted at the prompt or in scripts.

I get the above error, can anyone help ? I am using MATLAB 7.6.0(2008a). Thanks

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19 Apr 2010 Jenn Risk

### Jenn Risk (view profile)

Very helpful optically - but can it calculate the area of the error ellipse? I couldn't easily get it to adapt to this. Any help would be great!

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18 Nov 2009 David

### David (view profile)

Sorry, but my previous comment contained some errors:
- C = [1 -2; -2; 4]. This is not a valid covariance matrix.
- "positive semi-definite symmetric (that is, they may include negative values off the diagonal)." This is not true.

What is true, is that C must be a positive semi-definite matrix. But that is just a minor comment, because the implementation allows for that.

Conclusion:
This Matlab function works. Thanks!

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17 Nov 2009 David

### David (view profile)

% NOTES: C must be positive definite for this function to
% work properly.

This is quite a strange restriction, because covariance matrices are positive semi-definite symmetric (that is, they may include negative values off the diagonal). For example, it is not possible to visualize the following very simple, and valid, covariance matrix: C = [1 -2; -2; 4].

Does anybody know of a Matlab function which is capable of visualizing all kinds of covariance matrices (both 2D and 3D)? Thanks!

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16 Nov 2009 Pearl

### Pearl (view profile)

16 Nov 2009 Benjamin Pavie

### Benjamin Pavie (view profile)

01 Sep 2009 Miguel Torres

01 Jul 2009 Nora

02 Dec 2008 John

### John (view profile)

function works great and is easy to use. thank you

12 Nov 2008 Dan Stowell

### Dan Stowell (view profile)

Delightful tool, easy to use and worked straight away

17 Sep 2008 R Lewis

Did the job flawlessly.

06 Aug 2008 Alex Yakubovich

re: change color, multiple ellipses on same plot

To have multiple ellipses, just type 'hold on' in the command window before calling error_ellipse. You can change the color once you've plotted the ellipse in the property editor (open pe in view>property editor)

precisely what i needed! hooray.

21 Jun 2008 M ChC

how do I change the color of the ellipse?

04 Jun 2008 Dagmar Schoch
15 May 2008 Trevor Wood

excellent, thanks.

26 Apr 2008 Marino Pagan

Thank you very much!!! Excellent!

11 Apr 2008 Matthew Nelson

very useful. thank you

21 Feb 2008 phil fox

Be aware that the default confidence interval is 0.5 rather than more standard values such as 0.683, 0.9 etc.. Use the 'conf' parameter to change.

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21 Nov 2007 Volkan Ozturk

How can i see two plots on the same graphics. I have to do some comparison.

Regards

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03 Jul 2007 kevin chen

handy

25 Jun 2007 Feng Rice

Excellent.

10 Jan 2007 mohan palani
02 Nov 2006 Sujai Kumar
14 Jul 2006 John Magirk

perfect! works great AND easy to use.

05 Jul 2006 Chris Willy

Great code, very useful. Saved me lots of time.

16 May 2006 Matt Irwin

Great code, thanks.

10 May 2006 Damien Dusha

You just saved me a day and most of my hair :)

04 May 2006 Valentin Kuklin

Amazing. Good work! Thanks a lot!

09 Apr 2006 M Fellows

Very Useful!

27 Feb 2006 ryan jessup

worked perfectly! Thanks!

06 Feb 2006 oxana govokhina

Excellent

24 Jan 2006 Laurent Nguyen

Works perfectly

14 Oct 2005 Juan Pablo Nieto

It works excellent

21 Mar 2005 Paul Thompson

There is NOT an error at line 117.

05 Jan 2005 Kamini Singha

works fabulously.

02 Dec 2004 Niklaus Hugi
29 Jul 2004 Gordon Dryden

There is an error at line 117. The line reads: XYZ = [X(:),Y(:),Z(:)]*sqrt(eigval)*eigvec'; but should be: XYZ = [X(:),Y(:),Z(:)]*eigvec*sqrt(eigval)*eigvec';

13 Apr 2004 Mark Brown

Doesn't run. I get an error...
??? Undefined command/function 'getopt'.
Error in ==> error_ellipse at 61
prop = getopt(default_properties, varargin{:});

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13 Apr 2004 Una Kusan

Now it's working fine.
Thanks again!
U.

07 Apr 2004 Una Kusan

It doesn't work on my matlab platform (6.1).

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