/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   http://lammps.sandia.gov, Sandia National Laboratories
   Steve Plimpton, sjplimp@sandia.gov

   Copyright (2003) Sandia Corporation.  Under the terms of Contract
   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
   certain rights in this software.  This software is distributed under 
   the GNU General Public License.

   See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */

/* ----------------------------------------------------------------------
   Contributing authors: Mike Brown (ORNL), brownw@ornl.gov
------------------------------------------------------------------------- */

#ifndef GB_GPU_KERNEL
#define GB_GPU_KERNEL

#ifdef NV_KERNEL
#include "gb_gpu_extra.h"
#endif

__inline void compute_eta_torque(numtyp m[9],numtyp m2[9], const numtyp4 shape, 
                                 numtyp ans[9])
{
  numtyp den = m[3]*m[2]*m[7]-m[0]*m[5]*m[7]-
    m[2]*m[6]*m[4]+m[1]*m[6]*m[5]-
    m[3]*m[1]*m[8]+m[0]*m[4]*m[8];
  den = (numtyp)1.0/den;
  
  ans[0] = shape.x*(m[5]*m[1]*m2[2]+(numtyp)2.0*m[4]*m[8]*m2[0]-
		    m[4]*m2[2]*m[2]-(numtyp)2.0*m[5]*m2[0]*m[7]+
		    m2[1]*m[2]*m[7]-m2[1]*m[1]*m[8]-
		    m[3]*m[8]*m2[1]+m[6]*m[5]*m2[1]+
		    m[3]*m2[2]*m[7]-m2[2]*m[6]*m[4])*den;
  
  ans[1] = shape.x*(m[2]*m2[0]*m[7]-m[8]*m2[0]*m[1]+
		    (numtyp)2.0*m[0]*m[8]*m2[1]-m[0]*m2[2]*m[5]-
		    (numtyp)2.0*m[6]*m[2]*m2[1]+m2[2]*m[3]*m[2]-
		    m[8]*m[3]*m2[0]+m[6]*m2[0]*m[5]+
		    m[6]*m2[2]*m[1]-m2[2]*m[0]*m[7])*den;
  
  ans[2] = shape.x*(m[1]*m[5]*m2[0]-m[2]*m2[0]*m[4]-
		    m[0]*m[5]*m2[1]+m[3]*m[2]*m2[1]-
		    m2[1]*m[0]*m[7]-m[6]*m[4]*m2[0]+
		    (numtyp)2.0*m[4]*m[0]*m2[2]-(numtyp)2.0*m[3]*m2[2]*m[1]+
		    m[3]*m[7]*m2[0]+m[6]*m2[1]*m[1])*den;
  
  ans[3] = shape.y*(-m[4]*m2[5]*m[2]+(numtyp)2.0*m[4]*m[8]*m2[3]+
		    m[5]*m[1]*m2[5]-(numtyp)2.0*m[5]*m2[3]*m[7]+
		    m2[4]*m[2]*m[7]-m2[4]*m[1]*m[8]-
		    m[3]*m[8]*m2[4]+m[6]*m[5]*m2[4]-
		    m2[5]*m[6]*m[4]+m[3]*m2[5]*m[7])*den;
  
  ans[4] = shape.y*(m[2]*m2[3]*m[7]-m[1]*m[8]*m2[3]+
		    (numtyp)2.0*m[8]*m[0]*m2[4]-m2[5]*m[0]*m[5]-
		    (numtyp)2.0*m[6]*m2[4]*m[2]-m[3]*m[8]*m2[3]+
		    m[6]*m[5]*m2[3]+m[3]*m2[5]*m[2]-
		    m[0]*m2[5]*m[7]+m2[5]*m[1]*m[6])*den;
  
  ans[5] = shape.y*(m[1]*m[5]*m2[3]-m[2]*m2[3]*m[4]-
		    m[0]*m[5]*m2[4]+m[3]*m[2]*m2[4]+
		    (numtyp)2.0*m[4]*m[0]*m2[5]-m[0]*m2[4]*m[7]+
		    m[1]*m[6]*m2[4]-m2[3]*m[6]*m[4]-
		    (numtyp)2.0*m[3]*m[1]*m2[5]+m[3]*m2[3]*m[7])*den;
  
  ans[6] = shape.z*(-m[4]*m[2]*m2[8]+m[1]*m[5]*m2[8]+
		    (numtyp)2.0*m[4]*m2[6]*m[8]-m[1]*m2[7]*m[8]+
		    m[2]*m[7]*m2[7]-(numtyp)2.0*m2[6]*m[7]*m[5]-
		    m[3]*m2[7]*m[8]+m[5]*m[6]*m2[7]-
		    m[4]*m[6]*m2[8]+m[7]*m[3]*m2[8])*den;
  
  ans[7] = shape.z*-(m[1]*m[8]*m2[6]-m[2]*m2[6]*m[7]-
		     (numtyp)2.0*m2[7]*m[0]*m[8]+m[5]*m2[8]*m[0]+
		     (numtyp)2.0*m2[7]*m[2]*m[6]+m[3]*m2[6]*m[8]-
		     m[3]*m[2]*m2[8]-m[5]*m[6]*m2[6]+
		     m[0]*m2[8]*m[7]-m2[8]*m[1]*m[6])*den;
  
  ans[8] = shape.z*(m[1]*m[5]*m2[6]-m[2]*m2[6]*m[4]-
		    m[0]*m[5]*m2[7]+m[3]*m[2]*m2[7]-
		    m[4]*m[6]*m2[6]-m[7]*m2[7]*m[0]+
		    (numtyp)2.0*m[4]*m2[8]*m[0]+m[7]*m[3]*m2[6]+
		    m[6]*m[1]*m2[7]-(numtyp)2.0*m2[8]*m[3]*m[1])*den;
}

__kernel void kernel_gayberne(__global numtyp4* x_,__global numtyp4 *q,
                              __global numtyp4* shape, __global numtyp4* well, 
                              __global numtyp *gum, __global numtyp2* sig_eps, 
                              const int ntypes, __global numtyp *lshape, 
                              __global int *dev_nbor, const int stride, 
                              __global acctyp4 *ans, const int astride, 
                              __global acctyp *engv, __global int *err_flag, 
                              const int eflag, const int vflag, const int inum,
                              const int nall) {
  __local numtyp sp_lj[4];

  // ii indexes the two interacting particles in gi
  int ii=THREAD_ID_X;
  if (ii<4)
    sp_lj[ii]=gum[ii+3];    
  ii+=mul24((int)BLOCK_ID_X,(int)BLOCK_SIZE_X);                                  
  __syncthreads();

  if (ii<inum) {

  acctyp energy=(acctyp)0;
  acctyp4 f;
  f.x=(acctyp)0;
  f.y=(acctyp)0;
  f.z=(acctyp)0;
  acctyp4 tor;
  tor.x=(acctyp)0;
  tor.y=(acctyp)0;
  tor.z=(acctyp)0;
  acctyp virial[6];
  for (int i=0; i<6; i++)
    virial[i]=(acctyp)0;
  
  __global int *nbor=dev_nbor+ii;
  int i=*nbor;
  nbor+=stride;
  int numj=*nbor;
  nbor+=stride;
  __global int *nbor_end=nbor+mul24(stride,numj);
  
  numtyp4 ix=x_[i];
  int itype=ix.w;
  numtyp a1[9], b1[9], g1[9];
  numtyp4 ishape=shape[itype];
  {
    numtyp t[9];
    gpu_quat_to_mat_trans(q,i,a1);
    gpu_times3(ishape,a1,t);
    gpu_transpose_times3(a1,t,g1);
    gpu_times3(well[itype],a1,t);
    gpu_transpose_times3(a1,t,b1);
  }

  numtyp factor_lj;
  for ( ; nbor<nbor_end; nbor+=stride) {

  int j=*nbor;
  if (j < nall) 
    factor_lj = (numtyp)1.0;
  else {
    factor_lj = sp_lj[j/nall];
    j %= nall;
  }
  numtyp4 jx=x_[j];
  int jtype=jx.w;

  // Compute r12
  numtyp r12[3];
  r12[0] = jx.x-ix.x;
  r12[1] = jx.y-ix.y;
  r12[2] = jx.z-ix.z;
  numtyp ir = gpu_dot3(r12,r12);

  ir = rsqrt(ir);
  numtyp r = (numtyp)1.0/ir;

  numtyp a2[9];
  gpu_quat_to_mat_trans(q,j,a2);
  
  numtyp u_r, dUr[3], tUr[3], eta, teta[3];
  { // Compute U_r, dUr, eta, and teta
    // Compute g12
    numtyp g12[9];
    {
      numtyp g2[9];
      {
          gpu_times3(shape[jtype],a2,g12);
          gpu_transpose_times3(a2,g12,g2);
          gpu_plus3(g1,g2,g12);
      }
  
      { // Compute U_r and dUr
    
        // Compute kappa
        numtyp kappa[3];
        gpu_mldivide3(g12,r12,kappa,err_flag);

        // -- replace r12 with r12 hat
        r12[0]*=ir;
        r12[1]*=ir;
        r12[2]*=ir;

        // -- kappa is now / r
        kappa[0]*=ir;
        kappa[1]*=ir;
        kappa[2]*=ir;
  
        // energy
  
        // compute u_r and dUr
        numtyp uslj_rsq;
        {
          // Compute distance of closest approach
          numtyp h12, sigma12;
          sigma12 = gpu_dot3(r12,kappa);
          sigma12 = rsqrt((numtyp)0.5*sigma12);
          h12 = r-sigma12;

          // -- kappa is now ok
          kappa[0]*=r;
          kappa[1]*=r;
          kappa[2]*=r;
          
          int mtype=mul24(ntypes,itype)+jtype;
          numtyp sigma = sig_eps[mtype].x;
          numtyp epsilon = sig_eps[mtype].y;
          numtyp varrho = sigma/(h12+gum[0]*sigma);
          numtyp varrho6 = varrho*varrho*varrho;
          varrho6*=varrho6;
          numtyp varrho12 = varrho6*varrho6;
          u_r = (numtyp)4.0*epsilon*(varrho12-varrho6);

          numtyp temp1 = ((numtyp)2.0*varrho12*varrho-varrho6*varrho)/sigma;
          temp1 = temp1*(numtyp)24.0*epsilon;
          uslj_rsq = temp1*sigma12*sigma12*sigma12*(numtyp)0.5;
          numtyp temp2 = gpu_dot3(kappa,r12);
          uslj_rsq = uslj_rsq*ir*ir;

          dUr[0] = temp1*r12[0]+uslj_rsq*(kappa[0]-temp2*r12[0]);
          dUr[1] = temp1*r12[1]+uslj_rsq*(kappa[1]-temp2*r12[1]);
          dUr[2] = temp1*r12[2]+uslj_rsq*(kappa[2]-temp2*r12[2]);
        }

        // torque for particle 1
        {
          numtyp tempv[3], tempv2[3];
          tempv[0] = -uslj_rsq*kappa[0];
          tempv[1] = -uslj_rsq*kappa[1];
          tempv[2] = -uslj_rsq*kappa[2];
          gpu_row_times3(kappa,g1,tempv2);
          gpu_cross3(tempv,tempv2,tUr);
        }
      }
    }
     
    // Compute eta
    {
      eta = (numtyp)2.0*lshape[itype]*lshape[jtype];
      numtyp det_g12 = gpu_det3(g12);
      eta = pow(eta/det_g12,gum[1]);
    }
    
    // Compute teta
    numtyp temp[9], tempv[3], tempv2[3];
    compute_eta_torque(g12,a1,ishape,temp);
    numtyp temp1 = -eta*gum[1];

    tempv[0] = temp1*temp[0];
    tempv[1] = temp1*temp[1];
    tempv[2] = temp1*temp[2];
    gpu_cross3(a1,tempv,tempv2);
    teta[0] = tempv2[0];
    teta[1] = tempv2[1];
    teta[2] = tempv2[2];
  
    tempv[0] = temp1*temp[3];
    tempv[1] = temp1*temp[4];
    tempv[2] = temp1*temp[5];
    gpu_cross3(a1+3,tempv,tempv2);
    teta[0] += tempv2[0];
    teta[1] += tempv2[1];
    teta[2] += tempv2[2];

    tempv[0] = temp1*temp[6];
    tempv[1] = temp1*temp[7];
    tempv[2] = temp1*temp[8];
    gpu_cross3(a1+6,tempv,tempv2);
    teta[0] += tempv2[0];
    teta[1] += tempv2[1];
    teta[2] += tempv2[2];
  }
  
  numtyp chi, dchi[3], tchi[3];
  { // Compute chi and dchi

    // Compute b12
    numtyp b2[9], b12[9];
    {
      gpu_times3(well[jtype],a2,b12);
      gpu_transpose_times3(a2,b12,b2);
      gpu_plus3(b1,b2,b12);
    }

    // compute chi_12
    r12[0]*=r;
    r12[1]*=r;
    r12[2]*=r;
    numtyp iota[3];
    gpu_mldivide3(b12,r12,iota,err_flag);
    // -- iota is now iota/r
    iota[0]*=ir;
    iota[1]*=ir;
    iota[2]*=ir;
    r12[0]*=ir;
    r12[1]*=ir;
    r12[2]*=ir;
    chi = gpu_dot3(r12,iota);
    chi = pow(chi*(numtyp)2.0,gum[2]);

    // -- iota is now ok
    iota[0]*=r;
    iota[1]*=r;
    iota[2]*=r;

    numtyp temp1 = gpu_dot3(iota,r12);
    numtyp temp2 = (numtyp)-4.0*ir*ir*gum[2]*pow(chi,(gum[2]-(numtyp)1.0)/
                                                      gum[2]);
    dchi[0] = temp2*(iota[0]-temp1*r12[0]);
    dchi[1] = temp2*(iota[1]-temp1*r12[1]);
    dchi[2] = temp2*(iota[2]-temp1*r12[2]);

    // compute t_chi
    numtyp tempv[3];
    gpu_row_times3(iota,b1,tempv);
    gpu_cross3(tempv,iota,tchi);
    temp1 = (numtyp)-4.0*ir*ir;
    tchi[0] *= temp1;
    tchi[1] *= temp1;
    tchi[2] *= temp1;
  }

  numtyp temp2 = factor_lj*eta*chi;
  if (eflag>0)
    energy+=u_r*temp2;
  numtyp temp1 = -eta*u_r*factor_lj;
  if (vflag>0) {
    r12[0]*=-r;
    r12[1]*=-r;
    r12[2]*=-r;
    numtyp ft=temp1*dchi[0]-temp2*dUr[0];
    f.x+=ft;
    virial[0]+=r12[0]*ft;
    ft=temp1*dchi[1]-temp2*dUr[1];
    f.y+=ft;
    virial[1]+=r12[1]*ft;
    virial[3]+=r12[0]*ft;
    ft=temp1*dchi[2]-temp2*dUr[2];
    f.z+=ft;
    virial[2]+=r12[2]*ft;
    virial[4]+=r12[0]*ft;
    virial[5]+=r12[1]*ft;
  } else {
    f.x+=temp1*dchi[0]-temp2*dUr[0];
    f.y+=temp1*dchi[1]-temp2*dUr[1];
    f.z+=temp1*dchi[2]-temp2*dUr[2];
  }

  // Torque on 1
  temp1 = -u_r*eta*factor_lj;
  temp2 = -u_r*chi*factor_lj;
  numtyp temp3 = -chi*eta*factor_lj;
  tor.x+=temp1*tchi[0]+temp2*teta[0]+temp3*tUr[0];
  tor.y+=temp1*tchi[1]+temp2*teta[1]+temp3*tUr[1];
  tor.z+=temp1*tchi[2]+temp2*teta[2]+temp3*tUr[2];

  } // for nbor

  // Store answers
  __global acctyp *ap1=engv+ii;
  if (eflag>0) {
    *ap1=energy;
    ap1+=astride;
  }
  if (vflag>0) {
    for (int i=0; i<6; i++) {
      *ap1=virial[i];
      ap1+=astride;
    }
  }
  ans[ii]=f;
  ans[ii+astride]=tor;
  } // if ii
}

#endif