cflux: calculate flux

A convolution model to calculate the flux of other model components. For example:

cflux*phabs*(pow + gauss)with the normalization of the power-law model fixed to a non-zero value gives the flux and error on the entire model.

phabs*cflux*(pow + gauss)again with the normalization of the power-law fixed to a non-zero value gives the unabsorbed flux and error. Finally,

phabs*(pow + cflux*gauss)with the normalizaton of the gaussian fixed to a non-zero value gives the flux and error on the gaussian component. Note that when the cflux model is used the normalization of one of the additive models must be fixed to a non-zero value. It is also important to ensure that the energy range over which the model is calculated (which is determined by the response matrix in use) covers the energy range for which the flux is calculated. If the model to which the cflux is applied integrates to zero then a divide-by-zero error will occur resulting in NaN values for the fit statistic.

Parameters are:

par1=Emin | Minimum energy over which flux is calculated. |

par2=Emax | Maximum energy over which flux is calculated. |

par3=lg10Flux | log (base 10) flux in erg/cm/s |