Xraytrace documentation

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===== Material parameters =====


The materials used within the calculation are represented by materials table, which is
supplied as a an input file, defined at the same moment as the data are loaded (see the [[computational_domain|computational domain]] section).

This file has a simple structure - a set of entries for individual material indices,
defining how the system should get the material data. Each row starts by material index (to match
the indices in the VTK file or vector file defining the [[sample_geometry|sample geometry)]].
Then, material type is listed (0 for direct definition of n, k, density and attenuation, 99 for use of the xraylib database). For material type = 0 the further four values are real and imaginary part of the refractive index, density (in g/cm3) and attenuation coefficient.
For material type = 99 the element or compound chemical formula is written. Moreover we have two parameters that
can be used to force the system to use different values of attenuation coefficient and density than those
calculated from the Xraylib database. This is most usually not needed and can be left zero to get them from Xraylib.

An example of the materials file entries is shown below:
<code>
0 0 1 0 0 0
1 0 0.9999 2 3 4
2 99 Si 0 0
3 99 Cr 0 0
</code>


A second option how to override the density of the material loaded from library
is to use the following directive in the main parameter file:
<code>
OVERRIDE_XRAYLIB_DENSITY
index value
</code>
which uses the supplied density for the particular index, but calculates everything using Xraylib as usual based on this density.

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