Hi,
They are both relevant. The valid flag tells you have reached a minimum, but the minimiser status returns (for some of the minimiser such as Minuit) more information.
For example using Minuit2 you have as status:
- status = 1 : Covariance was made pos defined
- status = 2 : Hesse is invalid
- status = 3 : Edm is above max
- status = 4 : Reached call limit
- status = 5 : Covariance is not positive defined
For status=0 or 1 the fitted status will be valid, while in the other cases (status=2,3,4,5) it will not be.
Lorenzo