To better understand MINUIT, I have tried to fit a line using a negative log likelihood method. I am only executing the MIGRAD command. Below is the output. The last four items in the output are the best fit values for the two parameters and the true values of the two parameters. I am not sure why MIGRAD would fail to converge on such a simple example so I am wondering what I am doing wrong that might be causing this. Any help is much appreciated. If a working version of the code would be helpful, please let me know and I will be happy to provide it. Thank you for your time!

** 1 **SET ERRDEF 0.5

** 2 **SET STR 2

NOW USING STRATEGY 2: MAKE SURE MINIMUM TRUE, ERRORS CORRECT

PARAMETER DEFINITIONS:

NO. NAME VALUE STEP SIZE LIMITS

1 a[0] 2.00000e+00 1.00000e-01 no limits

2 a[1] 1.60000e+01 1.00000e-01 no limits

** 3 **MIGRAD 1e+04 100

FIRST CALL TO USER FUNCTION AT NEW START POINT, WITH IFLAG=4.

START MIGRAD MINIMIZATION. STRATEGY 2. CONVERGENCE WHEN EDM .LT. 1.00e-01

EIGENVALUES OF SECOND-DERIVATIVE MATRIX:

-2.8605e-02 2.0286e+00

MINUIT WARNING IN HESSE

============== MATRIX FORCED POS-DEF BY ADDING 0.030634 TO DIAGONAL.

FCN=2549.04 FROM HESSE STATUS=NOT POSDEF 30 CALLS 31 TOTAL

EDM=50436.7 STRATEGY= 2 ERR MATRIX NOT POS-DEF

EXT PARAMETER APPROXIMATE STEP FIRST

NO. NAME VALUE ERROR SIZE DERIVATIVE

1 a[0] 2.00000e+00 7.13730e-08 1.00000e-06 -2.67286e+09

2 a[1] 1.60000e+01 3.80075e-07 7.62939e-06 -3.34107e+08

ERR DEF= 0.5

MIGRAD FAILS TO FIND IMPROVEMENT

COVARIANCE MATRIX CALCULATED SUCCESSFULLY

FCN=2497.32 FROM HESSE STATUS=OK 14 CALLS 90 TOTAL

EDM=4495.17 STRATEGY= 2 ERROR MATRIX ACCURATE

EXT PARAMETER STEP FIRST

NO. NAME VALUE ERROR SIZE DERIVATIVE

1 a[0] 3.22085e+00 3.63636e-08 1.53582e-06 -1.62605e+09

2 a[1] 2.24987e+01 1.66290e-07 1.07282e-05 -2.32781e+08

ERR DEF= 0.5

MIGRAD FAILS TO FIND IMPROVEMENT

COVARIANCE MATRIX CALCULATED SUCCESSFULLY

FCN=2497.32 FROM HESSE STATUS=OK 18 CALLS 111 TOTAL

EDM=10488.7 STRATEGY= 2 ERROR MATRIX ACCURATE

EXT PARAMETER STEP FIRST

NO. NAME VALUE ERROR SIZE DERIVATIVE

1 a[0] 3.22085e+00 5.32309e-08 1.53582e-06 -1.62605e+09

2 a[1] 2.24987e+01 2.54012e-07 1.07282e-05 -2.32781e+08

ERR DEF= 0.5

MIGRAD FAILS TO FIND IMPROVEMENT

MIGRAD TERMINATED WITHOUT CONVERGENCE.

FCN=2497.32 FROM MIGRAD STATUS=FAILED 114 CALLS 115 TOTAL

EDM=10488.7 STRATEGY= 2 ERR MATRIX APPROXIMATE

EXT PARAMETER APPROXIMATE STEP FIRST

NO. NAME VALUE ERROR SIZE DERIVATIVE

1 a[0] 3.22085e+00 5.32309e-08 0.00000e+00 -1.62605e+09

2 a[1] 2.24987e+01 2.54012e-07 0.00000e+00 -2.32781e+08

ERR DEF= 0.5

EXTERNAL ERROR MATRIX. NDIM= 25 NPAR= 2 ERR DEF=0.5

2.834e-15 1.320e-14

1.320e-14 6.452e-14

ERR MATRIX APPROXIMATE

PARAMETER CORRELATION COEFFICIENTS

NO. GLOBAL 1 2

1 0.97590 1.000 0.976

2 0.97590 0.976 1.000

ERR MATRIX APPROXIMATE

Best a0 = 3.22085

Best a1 = 22.4987

a_true[0] = 2.68

a_true[1] = 16.74