NCrystal release 0.9.10

• This release represents a large amount of work in many areas, and in particular focusing on aspects of Bragg diffraction in single crystals.
• The Gaussian mosaicity modelling code was completely reimplemented, going back to the fundamental equations and making sure everything is carried out in a consistent and precise manner. Cross-section evaluation automatically selects between efficient numerical Romberg integrations and evaluation of new improved closed-form expressions, which takes the relevant spherically geometric into account. The code thus now gracefully handles everything from backscattering to forward scattering scenarios, and a large dynamic range of mosaicities, covering at least a range of 0.01arcseconds to tens of degrees. Despite this, computational speed is also improved, thanks to various enhancements and in particular faster code for searching through the available plane normals. A new parameter, mosprec, can be used to tune the tradeoff between precision and speed. The default value of 1e-3 is likely adequate for almost all users.
• Introducing a completely new and precise modelling of layered crystals, with the LCBragg class. This class, primarily intended to be used for modelling of Pyrolythic Graphite, by default takes the rotational aspects of such crystal into account using an from-first-principles approach to figuring out which sets of normals will contribute to the scattering cross-sections, and then finding the exact contribution through efficient numerical integrals. A crystal is considered to be a layered crystal if it has the lcaxis vector parameter set. Additionally, the lcmode parameter can be used to select slower reference parameters, which simply sample an SCBragg single-crystal instance many times, in different rotated systems.
• Huge speedup when modelling low-wavelength (<1Aa) neutrons in single crystals: Approximate the very large number of very weak and uninteresting scatter planes at 2*d-spacings < 1Aa with an isotropic mosaicity distribution, which is a rather appropriate approximation due to the very large number of very weak planes involved. The cutoff value of dspacing=0.5Aa can be modified with the new sccutoff parameter.
• Bragg diffraction in powders and polycrystals was never slow, but the PCbragg class was nonetheless rewritten to become even faster by working on energies directly, avoiding internal conversions to wavelength at each call.
• Embedded an NCRYSTALMATCFG[lcaxis=0,0,1] statement in the data file C_sg194_pyrolytic_graphite.ncmat, so that it will by default be modelled as a layered crystal with the correct rotation axis, which is likely what almost all users will want.
• Calling generateScattering where cross-sections are vanishing now generally leads to nothing happening (i.e. scatter_angle = 0 and delta_ekin=0) rather than the previous fallback of isotropic elastic scattering.
• Retire RandSimple and introduce instead RandXRSR implementing the xoroshiro128+ generator. This means that the fall-back RNG option shipped with NCrystal is now not only fast, but also fully suitable for scientific work.
• Fix bug in the NCrystal McStas component which resulted in wrong attenuation factors being calculated for the default absorption mode.
• Changed the conversion constants used in the McStas component in order to make unit conversion issues in the NCrystal-McStas interface less likely to produce undesired imprecision. Further discussions with McStas devs will be needed in order to completely address the issue.
• Code creating lattice rotation matrices was updated in order to avoid small rounding errors in the generated normals in most cases.
• More sanity checks and input pruning of atomic positions and lattice structure loaded from input files. Also improved robustness of .nxs file loading.
• Remove spurious ref-count increase in CalcBase::setRandomGenerator (thanks to A. Morozov for the report).
• Fix windows builds (see github issue #17). Many thanks to A. Morozov for a detailed report.
• Many general infrastructure improvements: Refactor random sampling algorithms from CalcBase objects (a necessary step for future enhanced MT support). Refactor orientation code from SCBragg (now used by both SCBragg and LCBragg). Refactor .ncmat loading code to disentangle the parsing code from the code. Lots of new utilities: Cubic splines, Romberg integration, root finding, derivative estimation. Single header NCDefs.hh providing all ubiquitous definitions and infrastructure related to memory handling and error reporting, and also handles includes which must get special treatment due to differences between platforms or C++ versions. Add UniquePtr (similar to C++11's unique_ptr). Add PlaneProvider (supported in PCBragg, SCBragg, LCBragg), for customizing which planes goes in which process. Avoid bind1st usage as it is removed in C++17. Custom functions for evaluating sine and cosine of angles in various ranges - between 5-10 times faster than the standard functions at 15 significant digits. Also add fast approximations for atan and exp. Performed careful changes to ncmin and ncmax functions with large performance implications (surprisingly, std::fmax generates very inefficient machine code: https://godbolt.org/g/Dxy52A ). Add helper class for efficiently generating sine and cosine values for all grid-points in a grid. PCBragg supports more custom constructors.