Please provide the following information:

ROOT Version: 5.34.36

Platform, compiler: 5.4.0

When accessing the covariance matrix from MINUIT via:

Double_t cova[8][8];

minuit->mnemat(&cova[0][0], 8);

the matrix only has the size of the non-fixed parameters and does not respect the parameter ordering.

For example, if I have 8 parameters and parameter with index 5 is fixed, I will get a 7x7 matrix where index five (cova[5][5] in my example) has the values that belong to parameter with index 6. Is there a way to force MINUIT to give the matrix back with in a more logical way? Am I doing something wrong?

Thanks.