Using Minuit with TGraph2DErrors class

From: <andreyk1_at_post.tau.ac.il>
Date: Mon, 17 Jul 2006 15:19:49 +0300

Dear rooters,

I'm trying to fit some complicated function using Minuit package and TGraph2DErrors class. The choise for Tgraph2DErrors is due to fitted function: it is a function of two variables (x,y).

It doesn't work properly, for exmaple, if I take a simple trial function, it gives a very good fit, but if I switch to another function, more compicated it fails. The result of fitting procedure is:

---

FCN=0.756195 FROM MIGRAD    STATUS=FAILED        263 CALLS         264 TOTAL
                     EDM=nan    STRATEGY= 1  ERROR MATRIX UNCERTAINTY 100.0 per
cent
  EXT PARAMETER                APPROXIMATE        STEP         FIRST
  NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE
   1  MU0          1.00000e+00           nan           nan           nan
   2  Omega_0      1.00000e+00   1.41421e+00           nan   0.00000e+00
   3  gam          1.00000e+00   1.41421e+00           nan   0.00000e+00
   4  A1           1.00000e+00   1.41421e+00           nan   0.00000e+00
   5  sss          1.00000e+00   1.41421e+00           nan   0.00000e+00



****************************************************************************

The parameters are unchanged (unity). But there should be an answer, because my function indeed has a minimum (from some assumptions). If I change it to only one parameter it is converged bu still gives unusefull answer (the initial parameter is remain unchanged):

---

FCN=0.756195 FROM MIGRAD    STATUS=CONVERGED      34 CALLS          35 TOTAL
                     EDM=nan    STRATEGY= 1      ERR MATRIX NOT POS-DEF
  EXT PARAMETER                APPROXIMATE        STEP         FIRST
  NO.   NAME      VALUE            ERROR          SIZE      DERIVATIVE
   1  MU0          1.00000e+00           nan   3.24730e+08           nan



****************************************************************************

Please, may be somebody can help me? Is there another method to fit a two-variable function?

Thanks,

        Andrew

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This message was sent using IMP, the Internet Messaging Program. Received on Mon Jul 17 2006 - 14:19:56 MEST