CDF's in GSL

[Rajarshi Guha <rajarshi at presidency dot com>]

Hello,
  I'm trying to to a chi square goodnes of fit on some of my data.

As far as I understand I need to use assume a distribution and calculate
the CDF. When I looked up the available CDF's I see that each
distribution provides two of them: P(X) & Q(x)

I'm a little confused as to which one I should be using. The manual
states that CDF's are clculated seperately for the upper and lower tails
- but how do I decide which CDF to use?

A related question is that when I report the final chi sq value the dof
is defined by (number of non empty cells) - (number of params in the
distribution) + 1

So say I use the gaussian CDF - that would imply that it is a two
parameter distribution. Is this correct. If so why does 
gsl_ran_gaussian() take only one parameter?

Thanks,

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Rajarshi Guha <rajarshi@presidency.com> <http://jijo.cjb.net>
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