Re: Fun with chisquares (more fits put on HST paper web page)

From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Sat Mar 22 2003 - 19:42:32 PST

  • Next message: Robert A. Knop Jr.: "Letting alpha vary (See HST paper site)"

    On Sat, Mar 22, 2003 at 05:12:02PM -0800, Greg Aldering wrote:
    > For 94361, 9579, 9624, and 9794, there is no obvious clue from the
    > SNminuit fit chi-square ratios Rob lists as to why the uncertainties
    > would change by much.

    Does this only happen once I'm fitting with a fixed zero, or does it
    happen even with the floating 0 but the new template?

    Fitting with a fixed zero could plausibly greatly reduce the uncertainty
    on the other parameters if there's a huge covariance between the zero
    level and the other parameters. If the zero level is fixed at zero,
    that may remove some of the freedom for the other parameters to vary.

    Note that the "primary fit" for this paper omits some of the worst
    offenders, and ends up with a rather better chisquare. The worst
    offenders that get thrown out are because their Ia status is in doubt:
    no real spectral confirmation.

    -Rob 

    -- 
--Prof. Robert Knop
  Department of Physics & Astronomy, Vanderbilt University
  robert.a.knop@vanderbilt.edu

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