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