
The parameters in this window are specific for the Takagi-Taupin (TT)
codes of the xcrystal_bent application.

They are ignored for the non-TT models.

Window [microns]:
	Set here the number of microns of "window".
	"Window" is the dimension of the integration network (Borrmann
	fan) along the crystal surface. 
	Other special values are accepted:
	0 = use the default value calculated internally by cryst_tt
	-X = means X times the default value. For example -0.2 means 
	that window is set to 20% of the default value.

Step [microns]:
        Set here the number of microns of "step".
        "Step" is the dimension of a step of the the integration network 
	(Borrmann fan) in the perpendicular direction of the crystal surface. 
        Other special values are accepted:
        0 = use the default value calculated internally by cryst_tt
        -X = means X times the default value. For example -2 means 
        that step is twice default value.

Write file with network?
	Allows to write a file (cryst_tt.net) containing the network and
	the electric field on that network.
	It can be siaplayed with Show/Takagi-Tapin/Integration Network 
	option.

Write file with all diff profiles?
	Allows to write a file (cryst_tt.all) containing the diffraction
	profiles in all the knots of the intersection between the
	integration network with the exit surface.
	It can be siaplayed with Show/Takagi-Tapin/All reflectivity curves 
	option.

RECOMMENDATIONS:

The network dimension incrteases when "window" increases, and also
increases when "sted" decreases. A carefull definition of these
parameters is essential. A large network can affect in an extremely long
calculation time. The calculation time can be estimated from the text
displayed in the spawned log screen. It is not possible to abort the
calculations from the interface. Long calculation may be aborted by
aborting the XOP session. Under Unix the process can be aborted from
another terminal window, by locating the process id (using ps -u
username | grep cryst) and killing such a process number (using kill).
Under Windows, the task can be aborted from the window that appears
when pressing <Ctl><Alt><Del> at the same time.

The diffraction profile is taken from the central point of the "window".
If "window" is too small, border effects can affect this main
diffraction profile. In order to check if the border effects are
important at the central point, one can display all thediffraction
profiles (in all the knot points) using the option:
Show/Takagi-Tapin/All reflectivity curves.

The "elem" should be small enough to avoid spurious oscillations and to
be able of following the phase of the diffracted beam. For example,
thin crystals may present Pendelloesung oscillations which period is 
completely wrong is "elem" is not correctly set.

They are not recipes for such values. The defaults set by cryst_tt are
calculated from the Pendelloesung length (l_pen):
  For Bragg/flat crystals:
    window = l_pen*400.0
    elem = window/100.0
  For Bragg/bent crystals:
    window = l_pen*120.0
    elem = window/50.0
  For Laue crystals:
    window = 3.0*(thickness+tan(thetab+alpha))
    elem=window/300.0

