Adjust one or more of the model parameters.
XSPEC> newpar [<index range> [<parameter spec list> or <coupling list>]]
where <parameter spec list> =:: <param value> <delta> <parameter range spec>, <parameter range spec> =:: <hard minimum> <soft minimum> <soft maximum> <hard maximum>, and <coupling list> =:: <" = " sign> <index coupled to first index> <multiplication factor for coupling> or <coupling list> =:: <" = " sign> <index coupled to first index> <" + " sign> <additive constant for coupling>. The model parameters are accessed through their model parameter indices. For example, the first parameter of the first model component generally is model parameter 1, etc. The first command line argument, <index range>, gives the indices' parameters to be modified by the newpar command. The default value is the range from the previous invocation of newpar. The remaining arguments can be used to update the parameter specification. If the parameter specification is omitted from the command line, then the user is explicitly prompted for it.
The first two arguments of the parameter specification are:
<param value> ! the trial value of the parameter used initially in the fit;
<delta> ! the "step size" used in the numerical determination of the derivatives used in the fitting process, when delta is set to zero, the parameter is not adjustable during the fit.
The four arguments of the range specification determine the range of acceptable values for the parameter. The soft limits should include the range of expected parameter behavior. Between the hard and soft limits, the parameter is made stiffer to adjustment by the minimization routine invoked by the f it command. The parameter never is allowed to have a value at or outside the hard limits. (One exception to this rule: the parameter can equal one of the hard limits if the soft limits have been placed outside the hard limit).
A carriage return or a slash (/) will terminate the input of the parameter specification. The series of prompted specification inputs can be explicitly terminated by an <EOF>.
Coupling of parameters allows two or more parameters in a model to always have the same value (or to differ by a constant multiplicative factor) and to have these coupled parameters free in the fit. An equal sign (=) after the <first index> indicates that coupling of parameters is desired. Then the <index coupled to first index> and a <multiplication factor for coupling> (default=1.0) follow.