| int | Bound | "B" When using pre-defined functions user parameter settings are used instead of default one |
| int | Chi2 | "X" For fitting THnsparse use chi2 method (default is likelihood) |
| int | Errors | "E" Performs a better error evaluation, calling HESSE and MINOS |
| int | Gradient | "G" Option to compute derivatives analytically |
| int | Integral | "I" Use function integral instead of function in center of bin |
| int | Like | "L" Use Log Likelihood. Default is chisquare method except fitting THnsparse |
| int | Minuit | "F" If fitting a polN, switch to minuit fitter |
| int | More | "M" Improve fit results. |
| int | NoErrX | "EX0" or "T" When fitting a TGraphErrors do not consider error in coordinates |
| int | Nochisq | "C" In case of linear fitting, don't calculate the chisquare |
| int | Nograph | "0" If set, do not display the function graph |
| int | Nostore | "N" If set, do not store the function graph |
| int | Plus | "+" Add new function (default is replace) |
| int | Quiet | "Q" Quiet mode. No print |
| int | Range | "R" Use the range stored in function |
| int | Robust | "ROB" or "H": For a TGraph use robust fitting |
| int | StoreResult | "S": Stores the result in a TFitResult structure |
| int | User | "U" Use a User specified fitting algorithm (via SetFCN) |
| int | Verbose | "V" Verbose mode. Print results after each iteration |
| int | W1 | "W" Set all the weights to 1. Ignore error bars |
| double | hRobust | value of h parameter used in robust fitting |
