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##

recorn: change correction norm for a spectrum

This model is a replacement for and improvement on the old xspec command
recornrm. If a correction file is in use for a spectrum then its normalization
can be fitted for using this model. The first parameter, which is not
variable, is the spectrum number and the second the correction file
normalization. The starting value of the second parameter should be set to
the current value of the correction file norm (this can be independently
set using the cornorm command).

Note that in order to fit the cornorm parameter, the
USE_NUMERICAL_DIFFERENTIATION setting in the user's Xspec.init start-up file
must be set to `true`. This causes XSPEC to use a slower full
numerical differentiation algorithm when calculating parameter derivatives
during a fit, and therefore is not recommended for general usage.

par1 |
specnum: spectrum number |

par2 |
cornorm: correction file normalization |