Re: Cash statistic fitting bug?

From: Michael Nowak <mnowak_at_email.domain.hidden>
Date: Tue, 30 Jul 2013 12:14:04 -0400
On Jul 30, 2013, at 12:04 PM, Moritz Boeck <moritz.boeck_at_email.domain.hidden
> It seems that this statistic in combination with a gradient minimization algorithm (at the moment we just verified it with the lmdif and mpfit fit method) leads to (slightly) wrong best fit parameter values.

This is a long standing, known issue in ISIS, Sherpa, and XSPEC.  lmdif/mpfit have chi^2 (and rational variants thereof) "hard wired" into them.  Cash, not being of a chi^2 form, needs a different form.

This was once upon a time on the web pages for all these systems giving this warning.  Although perhaps these warnings have slipped off into the annals of antiquity.

-Mike



----
You received this message because you are
subscribed to the isis-users list.
To unsubscribe, send a message to
isis-users-request_at_email.domain.hiddenwith the first line of the message as:
unsubscribe
Received on Tue Jul 30 2013 - 12:14:19 EDT

This archive was generated by hypermail 2.2.0 : Wed Jul 31 2013 - 15:42:57 EDT