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LSSTDESC / tomo_challenge

2020 Tomographic binning challenge
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Constant covariance assumption #37

Open dkirkby opened 4 years ago

dkirkby commented 4 years ago

It looks like the (Omega_c, sigma8) and (w0, wa) FoM values are calculated from a Fisher matrix that is assumed to have constant covariance, i.e., the tr[Cinv . grad(C, i) . Cinv . grad(C, j)]/2 term is not included.

Has someone already estimated the impact of this approximation on the results? How feasible is it to use the full Fisher matrix?

joezuntz commented 4 years ago

Hi David,

For 2-pt correlation functions like this the current behaviour is the standard thing to do, and Tilman has recently (in another context) drawn my attention to a paper showing that it's actually the correct thing to do, since otherwise you include artificial information that's not actually valid: https://arxiv.org/abs/1204.4724 .

Cheers, Joe

damonge commented 4 years ago

And we checked this explicitly for non-Gaussian fields in LSST here: https://arxiv.org/abs/1811.11584