Perform a fit while stepping the value of a parameter through a given range. Useful for determining confidence ranges in situations where greater control is needed than given with the error command.
XSPEC> steppar <step spec> [<step spec>...]
where <step spec> ::= [{log | nolog}] [{current | best}]
<param index>
<low value> <high value> <# steps>.
The parameter is stepped from <low value> to
<high value> in <# steps> plus one trials. The stepping is
either linear or log. Initially, the stepping is linear but it can be
changed by the optional string log before the parameter
index. nolog will force the stepping to be returned to the linear
form. The number of steps is set initially to 10. At each value, the
parameter is frozen, a fit performed, and the resulting value of
chi-squared given. If best is given as an argument then the
non-stepped parameters are reset to the best-fit values at each grid
point. Alternatively, if current is given as an argument then the
non-stepped parameters are started at their values after the last grid
point (the default).
If multiple <step spec> are given for different parameters, then a raster scan of the parameter ranges is performed. At the end of the set, the parameters and chi-squared are restored to the values they had initially.