Dear ROOT Support,
I am getting quite different results when I use different versions of ROOT (specifically I am comparing versions 5.30.01 and 5.34.18) to fit a series of points using user defined functions. There are no random numbers involved and the parameters of the fitted functions are set before starting the fitting. Since the function I am interested in is a ratio of the fitted functions, the final answer varies a lot depending on the version.
I attach the results of four fits obtained with these two versions.
Thank you very much,
Lluïsa-Maria Mir
Result fit version 5.30:
FCN=10.5114 FROM MIGRAD STATUS=CONVERGED 188 CALLS 189 TOTAL
EDM=1.53445e-06 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 p0 4.28200e-01 4.21612e-03 6.01480e-06 3.09649e-02
2 p1 2.95590e+01 1.33022e-01 1.70666e-04 -1.13795e-02
3 p2 3.50694e+00 2.06480e-01 1.89755e-04 8.79147e-03
4 p3 -1.89518e-03 2.10370e-03 2.10718e-06 3.14785e-02
FCN=33.2822 FROM MIGRAD STATUS=CONVERGED 272 CALLS 273 TOTAL
EDM=5.97285e-07 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 p0 4.34949e-01 3.12550e-03 8.38926e-06 -2.27878e-02
2 p1 2.95035e+01 1.46769e-01 3.18666e-04 1.03219e-03
3 p2 3.35821e+00 2.02380e-01 4.36793e-04 -6.26310e-04
4 p3 4.31720e-04 6.87747e-04 1.89047e-06 -1.62217e+00
FCN=15.2701 FROM MIGRAD STATUS=CONVERGED 180 CALLS 181 TOTAL
EDM=6.92992e-10 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 p0 3.04633e-01 5.02138e-03 1.90110e-06 1.98902e-02
2 p1 2.92176e+01 1.27168e-01 1.51640e-04 1.71361e-05
3 p2 1.58829e+00 1.65177e-01 5.34903e-05 -4.93301e-04
4 p3 4.03695e-01 4.24421e-03 2.50380e-06 -5.92528e-03
FCN=54.5345 FROM MIGRAD STATUS=CONVERGED 571 CALLS 572 TOTAL
EDM=2.32376e-09 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 p0 2.93572e-01 3.20097e-03 1.67422e-06 -8.34153e-02
2 p1 2.90771e+01 1.00317e-01 2.68336e-04 -7.35937e-04
3 p2 1.07134e+00 1.28410e-01 6.57540e-05 2.07551e-03
4 p3 4.22678e-01 3.03188e-03 2.40535e-06 4.72495e-02
Result fit version 5.34:
FCN=5.59966 FROM MIGRAD STATUS=CONVERGED 634 CALLS 635 TOTAL
EDM=1.15133e-08 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 p0 4.29939e-01 4.43409e-03 5.04147e-06 1.03256e-02
2 p1 2.99867e+01 6.16544e-01 5.72533e-04 2.86150e-04
3 p2 3.87209e+00 8.39471e-01 4.21262e-04 -1.87152e-04
4 p3 -4.71541e-04 1.27028e-03 7.15028e-07 -4.98167e-02
FCN=6.66434 FROM MIGRAD STATUS=CONVERGED 521 CALLS 522 TOTAL
EDM=8.57748e-08 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 p0 4.38657e-01 3.21688e-03 4.09106e-06 6.81716e-02
2 p1 3.01343e+01 4.73452e-01 5.83291e-04 -2.58046e-04
3 p2 3.95941e+00 6.06292e-01 5.39098e-04 -4.33914e-04
4 p3 1.45770e-04 1.44423e-03 1.20503e-06 -2.71034e-01
FCN=7.97357 FROM MIGRAD STATUS=CONVERGED 194 CALLS 195 TOTAL
EDM=2.87648e-07 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 p0 2.94811e-01 7.41518e-03 3.92089e-06 -8.92265e-03
2 p1 2.94033e+01 4.68338e-01 5.45125e-04 -1.19489e-03
3 p2 1.26040e+00 3.31219e-01 1.50790e-04 -6.51364e-04
4 p3 4.15759e-01 6.19198e-03 5.57059e-06 -6.06043e-02
FCN=15.0046 FROM MIGRAD STATUS=CONVERGED 447 CALLS 448 TOTAL
EDM=2.30393e-09 STRATEGY= 1 ERROR MATRIX ACCURATE
EXT PARAMETER STEP FIRST
NO. NAME VALUE ERROR SIZE DERIVATIVE
1 p0 3.02429e-01 7.26848e-03 5.25862e-06 -6.74100e-04
2 p1 2.94925e+01 4.72808e-01 7.25775e-04 -3.12319e-05
3 p2 1.38165e+00 3.26020e-01 2.12258e-04 2.18800e-04
4 p3 4.22231e-01 6.28783e-03 7.48109e-06 1.60846e-02