Chi2fit.Fit.chi2

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chi2(observables, fun, penalties \\ fn _ -> 0.0 end, options \\ [])

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Specs

chi2(observables(), (float() -> float()), (float() -> float()), Keyword.t()) ::
  float()

Calculates the Chi-squared function for a list of observables.

The observables are given as a list. Each observation has an error associated with it. The errors can be either symmetric or asymmetric.

A 'penalties'-function is used to assign penalties and these contribute to the chi-squared function. It may be used to 'forbid' certain parameter, x combinations.

Options

`model` - Required. Determines the contribution to chi-squared taking the asymmetric errors into account.
        Vaid values are `:linear`, `:simple`, and `:asimple`. See Errors below

Errors

`simple` - Use for asymmetric errors when the sigma+ and sigma- are close to each other
`asimple` - Use for asymmetric errors when y-values are not bound.
`linear` - Use this model when the y-values ar bound between 0 and 1. Linear transformation that:
    - is continuous in u=0,
    - passes through the point sigma+ at u=1,
    - asymptotically reaches 1-y at u->infinity
    - pass through the point -sigma- at u=-1,
    - asymptotically reaches -y at u->-infinity

Examples

iex> fun = &(&1)
...> chi2 [{0,3,1}], fun
9.0

iex> fun = &(&1)
...> chi2 [{0,3,1},{1,7,1},{2,3,1}], fun
46.0

iex> fun = &(&1)
...> chi2 [{0,3,3},{1,7,1},{2,3,1}], fun
38.0

iex> fun = &(&1-2)
...> chi2 [{0,3,1}], fun
25.0

end