/* -*- c++ -*- ----------------------------------------------------------
 *
 *                    *** Smooth Mach Dynamics ***
 *
 * This file is part of the USER-SMD package for LAMMPS.
 * Copyright (2014) Georg C. Ganzenmueller, georg.ganzenmueller@emi.fhg.de
 * Fraunhofer Ernst-Mach Institute for High-Speed Dynamics, EMI,
 * Eckerstrasse 4, D-79104 Freiburg i.Br, Germany.
 *
 * ----------------------------------------------------------------------- */

#ifndef SMD_KERNEL_FUNCTIONS_H_
#define SMD_KERNEL_FUNCTIONS_H_

namespace SMD_Kernels {
static inline double Kernel_Wendland_Quintic_NotNormalized(const double r, const double h) {
        if (r < h) {
                double q = 2.0 * r / h;
                return pow(1.0 - 0.5 * q, 4) * (2.0 * q + 1.0);
        } else {
                return 0.0;
        }
}

static inline double Kernel_Cubic_Spline(const double r, const double h) {
        double q = 2.0 * r / h;
        if (q > 2.0) {
                return 0.0;
        } else if ((q <= 2.0) && (q > 1.0)) {
                return pow(2.0 - q, 3.0) / 6.0;
        } else if ((q >= 0.0) && (q <= 1.0)) {
                return 2. / 3. - q * q + 0.5 * q * q * q;
        } else {
                return 0.0;
        }
}

static inline double Kernel_Barbara(const double r, const double h) {
        double arg = (1.570796327 * (r + h)) / h;
        double hsq = h * h;
        //wf = (1.680351548 * (cos(arg) + 1.)) / hsq;
        return -2.639490040 * sin(arg) / (hsq * h);
}

static inline void spiky_kernel_and_derivative(const double h, const double r, const int dimension, double &wf, double &wfd) {

        /*
         * Spiky kernel
         */

        if (r > h) {
                printf("r=%f > h=%f in Spiky kernel\n", r, h);
                wf = wfd = 0.0;
                return;
        }

        double hr = h - r; // [m]
        if (dimension == 2) {
                double n = 0.3141592654e0 * h * h * h * h * h; // [m^5]
                wfd = -3.0e0 * hr * hr / n; // [m*m/m^5] = [1/m^3] ==> correct for dW/dr in 2D
                wf = -0.333333333333e0 * hr * wfd; // [m/m^3] ==> [1/m^2] correct for W in 2D
        } else {
                wfd = -14.0323944878e0 * hr * hr / (h * h * h * h * h * h); // [1/m^4] ==> correct for dW/dr in 3D
                wf = -0.333333333333e0 * hr * wfd; // [m/m^4] ==> [1/m^3] correct for W in 3D
        }

        // alternative formulation
//              double hr = h - r;
//
//              /*
//               * Spiky kernel
//               */
//
//              if (domain->dimension == 2) {
//                      double h5 = h * h * h * h * h;
//                      wf = 3.183098861e0 * hr * hr * hr / h5;
//                      wfd = -9.549296583 * hr * hr / h5;
//
//              } else {
//                      double h6 = h * h * h * h * h * h;
//                      wf = 4.774648292 * hr * hr * hr / h6;
//                      wfd = -14.32394487 * hr * hr / h6;
//              }
//      }

}

static inline void barbara_kernel_and_derivative(const double h, const double r, const int dimension, double &wf, double &wfd) {

        /*
         * Barbara kernel
         */

        double arg = (1.570796327 * (r + h)) / h;
        double hsq = h * h;

        if (r > h) {
                printf("r = %f > h = %f in barbara kernel function\n", r, h);
                exit(1);
                //wf = wfd = 0.0;
                //return;
        }

        if (dimension == 2) {
                wf = (1.680351548 * (cos(arg) + 1.)) / hsq;
                wfd = -2.639490040 * sin(arg) / (hsq * h);
        } else {
                wf = 2.051578323 * (cos(arg) + 1.) / (hsq * h);
                wfd = -3.222611694 * sin(arg) / (hsq * hsq);
        }
}

/*
 * compute a normalized smoothing kernel only
 */
static inline void Poly6Kernel(const double hsq, const double h, const double rsq, const int dimension, double &wf) {

        double tmp = hsq - rsq;
        if (dimension == 2) {
                wf = tmp * tmp * tmp / (0.7853981635e0 * hsq * hsq * hsq * hsq);
        } else {
                wf = tmp * tmp * tmp / (0.6382918409e0 * hsq * hsq * hsq * hsq * h);
        }
}

/*
 * M4 Prime Kernel
 */

static inline void M4PrimeKernel(const double s, double &wf) {
        if (s < 1.0) {
                //wf = 1.0 - 2.5 * s * s + (3./2.) * s * s * s;
                wf = 1.0 - s * s *(2.5 -1.5 *s);
        } else if (s < 2.0) {
                //wf = 0.5 * (1.0 - s) * ((2.0 - s) * (2.0 - s));
                wf = 2.0 + (-4.0 + (2.5 - 0.5 * s)*s)*s;
        } else {
                wf = 0.0;
        }
}

}



#endif /* SMD_KERNEL_FUNCTIONS_H_ */
