This provides the shape of the XRT along the dispersion direction (integrated in cross-dispersion).

This function can have two modes of operations:

- Numerical integration of the parameterized PSF (see HIGH
accuracy level described in section 3.2.1)

This parameterization is numerically integrated along the cross-dispersion direction. - Dedicated parameterization

A dedicated set of parameters is provided that describes the PSF when integrated on the cross-dispersion direction. Gaussian and Lorentzian functions and a linear combination are allowed. The Gaussian parameterization has the form

with the parameters , , and provided by the CCF per Gaussian. Lorentzian parameterizations have the form

with the parameters , , and provided by the CCF per Lorentzian.The functions are selected by a flag in the CCF. The parameters of the centers ( and ) are given with respect to a common center to allow for an assymetric parameterizations. The common center is calculated by

The value of the input argument

`CENTER_CHAN`is added to , in order to provide the PSF correctly centered.

The width of the PSF of the telescope scales as a function of angle of
incidence on the gratings and diffration angle of the RGA by the
chromatic magnification function . The chromatic magnification
which is an imaging effect by the gratings that scales the width of
the PSF in the dispersion direction as a function of angle of
incidence and diffraction angle. It is defined as

and is an input argument.

The function returns the probability distribution which
calculated from by integration per channel

**Note:** The CAL inverts the parameterization that is in ` XRT_XPSF` along the dispersion axis, because the RGA acts as a
mirorr in this respect.