Add new library, which contains the calculation of the macroscopic quantities and a general cumulant computation. (Closes #13)

src/cpu/VirtualFluidsCore/LBM/CumulantK17LBMKernel.h

@@ -58,6 +58,11 @@ public:
     double getCalculationTime() override { return .0; }
 
 protected:
+    inline void forwardInverseChimeraWithK(LBMReal& mfa, LBMReal& mfb, LBMReal& mfc, LBMReal vv, LBMReal v2, LBMReal Kinverse, LBMReal K);
+    inline void backwardInverseChimeraWithK(LBMReal& mfa, LBMReal& mfb, LBMReal& mfc, LBMReal vv, LBMReal v2, LBMReal Kinverse, LBMReal K);
+    inline void forwardChimera(LBMReal& mfa, LBMReal& mfb, LBMReal& mfc, LBMReal vv, LBMReal v2);
+    inline void backwardChimera(LBMReal& mfa, LBMReal& mfb, LBMReal& mfc, LBMReal vv, LBMReal v2);
+
     virtual void initDataSet();
     LBMReal f[D3Q27System::ENDF + 1];
 
@@ -73,5 +78,70 @@ protected:
     LBMReal forcingX3;
 };
 
+////////////////////////////////////////////////////////////////////////////////
+//! \brief forward chimera transformation \ref forwardInverseChimeraWithK 
+//! Transformation from distributions to central moments according to Eq. (6)-(14) in
+//! <a href="https://doi.org/10.1016/j.jcp.2017.05.040"><b>[ M. Geier et al. (2017), DOI:10.1016/j.jcp.2017.05.040 ]</b></a>
+//! Modified for lower round-off errors.
+////////////////////////////////////////////////////////////////////////////////
+inline void CumulantK17LBMKernel::forwardInverseChimeraWithK(LBMReal& mfa, LBMReal& mfb, LBMReal& mfc, LBMReal vv, LBMReal v2, LBMReal Kinverse, LBMReal K)
+{
+    using namespace UbMath;
+    LBMReal m2 = mfa + mfc;
+    LBMReal m1 = mfc - mfa;
+    LBMReal m0 = m2 + mfb;
+    mfa = m0;
+    m0 *= Kinverse;
+    m0 += c1;
+    mfb = (m1 * Kinverse - m0 * vv) * K;
+    mfc = ((m2 - c2 * m1 * vv) * Kinverse + v2 * m0) * K;
+}
+////////////////////////////////////////////////////////////////////////////////
+//! \brief backward chimera transformation \ref backwardInverseChimeraWithK
+//! Transformation from central moments to distributions according to Eq. (57)-(65) in
+//! <a href="https://doi.org/10.1016/j.jcp.2017.05.040"><b>[ M. Geier et al. (2017), DOI:10.1016/j.jcp.2017.05.040 ]</b></a>
+//! ] Modified for lower round-off errors.
+////////////////////////////////////////////////////////////////////////////////
+inline void CumulantK17LBMKernel::backwardInverseChimeraWithK(LBMReal& mfa, LBMReal& mfb, LBMReal& mfc, LBMReal vv, LBMReal v2, LBMReal Kinverse, LBMReal K)
+{
+    using namespace UbMath;
+    LBMReal m0 = (((mfc - mfb) * c1o2 + mfb * vv) * Kinverse + (mfa * Kinverse + c1) * (v2 - vv) * c1o2) * K;
+    LBMReal m1 = (((mfa - mfc) - c2 * mfb * vv) * Kinverse + (mfa * Kinverse + c1) * (-v2)) * K;
+    mfc = (((mfc + mfb) * c1o2 + mfb * vv) * Kinverse + (mfa * Kinverse + c1) * (v2 + vv) * c1o2) * K;
+    mfa = m0;
+    mfb = m1;
+}
+////////////////////////////////////////////////////////////////////////////////
+//! \brief forward chimera transformation \ref forwardChimera 
+//! Transformation from distributions to central moments according to Eq. (6)-(14) in
+//! <a href="https://doi.org/10.1016/j.jcp.2017.05.040"><b>[ M. Geier et al. (2017), DOI:10.1016/j.jcp.2017.05.040 ]</b></a>
+//! for \f$ K_{abc}=0 \f$. This is to avoid unnessary floating point operations.
+//! Modified for lower round-off errors.
+////////////////////////////////////////////////////////////////////////////////
+inline void CumulantK17LBMKernel::forwardChimera(LBMReal& mfa, LBMReal& mfb, LBMReal& mfc, LBMReal vv, LBMReal v2)
+{
+    using namespace UbMath;
+    LBMReal m1 = (mfa + mfc) + mfb;
+    LBMReal m2 = mfc - mfa;
+    mfc = (mfc + mfa) + (v2 * m1 - c2 * vv * m2);
+    mfb = m2 - vv * m1;
+    mfa = m1;
+}
+////////////////////////////////////////////////////////////////////////////////
+//! \brief backward chimera transformation \ref backwardChimera 
+//! Transformation from central moments to distributions according to Eq. (57)-(65) in
+//! <a href="https://doi.org/10.1016/j.jcp.2017.05.040"><b>[ M. Geier et al. (2017), DOI:10.1016/j.jcp.2017.05.040 ]</b></a>
+//! for \f$ K_{abc}=0 \f$. This is to avoid unnessary floating point operations.
+//! Modified for lower round-off errors.
+////////////////////////////////////////////////////////////////////////////////
+inline void CumulantK17LBMKernel::backwardChimera(LBMReal& mfa, LBMReal& mfb, LBMReal& mfc, LBMReal vv, LBMReal v2)
+{
+    using namespace UbMath;
+    LBMReal ma = (mfc + mfa * (v2 - vv)) * c1o2 + mfb * (vv - c1o2);
+    LBMReal mb = ((mfa - mfc) - mfa * v2) - c2 * mfb * vv;
+    mfc = (mfc + mfa * (v2 + vv)) * c1o2 + mfb * (vv + c1o2);
+    mfb = mb;
+    mfa = ma;
+}
 
-#endif // CumulantK17LBMKernel_h__
\ No newline at end of file
+#endif // CumulantK17LBMKernel_h__