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Ivan Debono
Joined: 17 Apr 2007 Posts: 25 Affiliation: APC, Paris 7 / OBSPM

Posted: November 06 2008 


Does the iCosmo web interface Fisher matrix calculation use a 2point or 4point derivative by default? 

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Anais Rassat
Joined: 20 Oct 2004 Posts: 30 Affiliation: LASTRO (EPFL)

Posted: November 06 2008 


Hi Ivan,
The calculation on the web interface uses the 2point derivative.
The source code has the option to do both the 2point or 4point derivative, and you can download the source code here: http://www.icosmo.org/Initiative_Web/Tools.html
By default the source code does the calculation using the 2pointderivative, but this can be made more accurate by using a fiducial structure with:
fid = set_fiducial(calc_in=speed:0)
Cheers, Anais. 

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Walter Schrabmair
Joined: 29 Mar 2010 Posts: 1 Affiliation: Med Univ Graz

Posted: March 29 2010 


Dear Member,
I have studied the source to obtain the math schema how the fisher matrix is calculated. I discoverd that there are 2 methods. sne and boa. Do I assume correctly that the fisher matrix is calculated so?:
fisher = TRANSPOSE[DeriveMatrix] * INVERSE[covarianceMAtrix] * DeriveMatrix
Sorry for my stupid question: But what is the covariancematrix there? In teh source at boa the cov = INVERSE[fisher]. I am completely confused. Teh reson for my question are: in a book [Excel for chemists] there is written the attached picture (
and
).
CAN I SAY, that this P[i,j] is also the fisher matrix? But there I miss the covariance matrix. How is the covariacne matrix calculated? Thanks a lot for getting understand the fundamentals of the fisher calculation. 

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