Fisher matrix calculation

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
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Ivan Debono
Posts: 25
Joined: April 17 2007
Affiliation: APC, Paris 7 / OBSPM

Fisher matrix calculation

Post by Ivan Debono » November 06 2008

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

Anais Rassat
Posts: 24
Joined: October 20 2004
Affiliation: LASTRO (EPFL)

Fisher matrix calculation

Post by Anais Rassat » November 06 2008

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:

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.

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

Fisher matrix calculation

Post by Walter Schrabmair » 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 (

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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