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Fisher matrix calculation
 
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Ivan Debono



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

PostPosted: November 06 2008  Reply with quote

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



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

PostPosted: November 06 2008  Reply with quote

Hi Ivan,

The calculation on the web interface uses the 2-point derivative.

The source code has the option to do both the 2-point or 4-point 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 2point-derivative, 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

PostPosted: March 29 2010  Reply with quote

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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