conf()

From: Dmitry Svinkin <svinkin_at_email.domain.hidden>
Date: Tue, 23 Sep 2008 16:47:05 +0400
Hi!
I get underesimated single-parameter confidence limits when I try to compute
it by conf().

I use model "grbm(1)+0.0*constant(1)+0.0*constant(2)". And as a
fitting result I got such parameters:

isis> list_par;
grbm(1)+0.0*constant(1)+0.0*constant(2)
 idx  param           tie-to  freeze         value         min         max
  1  grbm(1).norm         0     1       0.03931449           0       1e+10
#=>  constant(1).factor/integrate_band(grbm(1).alpha,grbm(1).beta,grbm(1).tem,1.,20,7000,100.,1)
  2  grbm(1).alpha        0     0       -0.5793709          -3           2
  3  grbm(1).beta         0     0        -3.515191         -10           1
  4  grbm(1).tem          0     1         510.6869          50        1000  keV
#=>  constant(2).factor/(grbm(1).alpha+2.)
  5  constant(1).factor   0     0     5.950865e-06           0       1e+10
  6  constant(2).factor   0     0         725.4967           0       1e+10

Where integrate_band is a user defined function.

Next step is to get confidence limits of  parameters. Thereto I run, for
example, conf(2,1) to compue 68% conf limits.

isis> conf(2,0);
**** Lower confidence limit didn't converge[2]:  allow wider parameter ranges?
-0.534332
-0.579371

Also you can see that lower confidence limit is much smaller than upper
one. When I use grbm model without any functions in parameters all is
ok.

Can you explain, please, the root of such behavior?

Thanks.
Dmitriy

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Received on Tue Sep 23 2008 - 08:46:42 EDT

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