pair_smd_ulsph.cpp
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Created: Sun, Jun 2, 08:35

pair_smd_ulsph.cpp
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	/* ----------------------------------------------------------------------
	*
	* * 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.
	*
	* ----------------------------------------------------------------------- */

	/* ----------------------------------------------------------------------
	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.
	------------------------------------------------------------------------- */

	#include "math.h"
	#include "float.h"
	#include "stdlib.h"
	#include "string.h"
	#include "pair_smd_ulsph.h"
	#include "atom.h"
	#include "domain.h"
	#include "force.h"
	#include "update.h"
	#include "modify.h"
	#include "fix.h"
	#include "comm.h"
	#include "neighbor.h"
	#include "neigh_list.h"
	#include "neigh_request.h"
	#include "memory.h"
	#include "error.h"
	#include <stdio.h>
	#include <iostream>
	#include "smd_material_models.h"
	#include "smd_math.h"
	#include "smd_kernels.h"

	using namespace SMD_Kernels;
	using namespace std;
	using namespace LAMMPS_NS;
	using namespace SMD_Math;

	#include <Eigen/Eigen>
	using namespace Eigen;

	#define ARTIFICIAL_STRESS false
	#define FORMAT1 "%60s : %g\n"
	#define FORMAT2 "\n.............................. %s \n"

	PairULSPH::PairULSPH(LAMMPS *lmp) :
	Pair(lmp) {

	// per-type arrays
	Q1 = NULL;
	eos = viscosity = strength = NULL;
	c0_type = NULL;
	c0 = NULL;
	Lookup = NULL;
	artificial_stress = NULL;
	artificial_pressure = NULL;

	nmax = 0; // make sure no atom on this proc such that initial memory allocation is correct
	stressTensor = L = K = NULL;
	shepardWeight = NULL;
	smoothVel = NULL;
	numNeighs = NULL;
	F = NULL;
	rho = NULL;
	effm = NULL;

	velocity_gradient_required = false; // turn off computation of velocity gradient by default
	density_summation = velocity_gradient = false;

	comm_forward = 18; // this pair style communicates 18 doubles to ghost atoms
	updateFlag = 0;
	}

	/* ---------------------------------------------------------------------- */

	PairULSPH::~PairULSPH() {
	if (allocated) {
	//printf("... deallocating\n");
	memory->destroy(Q1);
	memory->destroy(rho0);
	memory->destroy(eos);
	memory->destroy(viscosity);
	memory->destroy(strength);
	memory->destroy(c0_type);
	memory->destroy(Lookup);
	memory->destroy(artificial_pressure);
	memory->destroy(artificial_stress);

	delete[] onerad_dynamic;
	delete[] onerad_frozen;
	delete[] maxrad_dynamic;
	delete[] maxrad_frozen;

	delete[] K;
	delete[] shepardWeight;
	delete[] c0;
	delete[] smoothVel;
	delete[] stressTensor;
	delete[] L;
	delete[] numNeighs;
	delete[] F;
	delete[] rho;
	delete[] effm;

	}
	}

	/* ----------------------------------------------------------------------
	*
	* Re-compute mass density from scratch.
	* Only used for plain fluid SPH with no physical viscosity models.
	*
	---------------------------------------------------------------------- */

	void PairULSPH::PreCompute_DensitySummation() {
	double *radius = atom->radius;
	double **x = atom->x;
	double *rmass = atom->rmass;
	int *type = atom->type;
	int ilist, jlist, *numneigh;
	int **firstneigh;
	int nlocal = atom->nlocal;
	int inum, jnum, ii, jj, i, itype, jtype, j;
	double h, irad, hsq, rSq, wf;
	Vector3d dx, xi, xj;

	// set up neighbor list variables
	inum = list->inum;
	ilist = list->ilist;
	numneigh = list->numneigh;
	firstneigh = list->firstneigh;

	// zero accumulators
	for (i = 0; i < nlocal; i++) {
	rho[i] = 0.0;
	//shepardWeight[i] = 0.0;
	}

	/*
	* only recompute mass density if density summation is used.
	* otherwise, change in mass density is time-integrated
	*/
	for (i = 0; i < nlocal; i++) {
	itype = type[i];
	if (setflag[itype][itype] == 1) {
	// initialize particle density with self-contribution.
	h = 2.0 * radius[i];
	hsq = h * h;
	Poly6Kernel(hsq, h, 0.0, domain->dimension, wf);
	rho[i] = wf * rmass[i]; // / shepardWeight[i];
	//printf("SIC to rho is %f\n", rho[i]);
	}
	}

	for (ii = 0; ii < inum; ii++) {
	i = ilist[ii];
	itype = type[i];
	jlist = firstneigh[i];
	jnum = numneigh[i];
	irad = radius[i];

	xi << x[i][0], x[i][1], x[i][2];

	for (jj = 0; jj < jnum; jj++) {
	j = jlist[jj];
	j &= NEIGHMASK;

	xj << x[j][0], x[j][1], x[j][2];
	dx = xj - xi;
	rSq = dx.squaredNorm();
	h = irad + radius[j];
	hsq = h * h;
	if (rSq < hsq) {

	jtype = type[j];
	Poly6Kernel(hsq, h, rSq, domain->dimension, wf);

	if (setflag[itype][itype] == 1) {
	rho[i] += wf * rmass[j]; // / shepardWeight[i];
	}

	if (j < nlocal) {
	if (setflag[jtype][jtype] == 1) {
	rho[j] += wf * rmass[i]; // / shepardWeight[j];
	}
	}
	} // end if check distance
	} // end loop over j
	} // end loop over i
	}

	/* ----------------------------------------------------------------------
	*
	* Compute shape matrix for kernel gradient correction and velocity gradient.
	* This is used if material strength or viscosity models are employed.
	*
	---------------------------------------------------------------------- */

	void PairULSPH::PreCompute() {
	double **atom_data9 = atom->smd_data_9;
	double *radius = atom->radius;
	double **x = atom->x;
	double **x0 = atom->x0;
	double **v = atom->vest;
	double *vfrac = atom->vfrac;
	int *type = atom->type;
	int ilist, jlist, *numneigh;
	int **firstneigh;
	int nlocal = atom->nlocal;
	int inum, jnum, ii, jj, i, itype, j, idim;
	double wfd, h, irad, r, rSq, wf, ivol, jvol;
	Vector3d dx, dv, g, du;
	Matrix3d Ktmp, Ltmp, Ftmp, K3di, D;
	Vector3d xi, xj, vi, vj, x0i, x0j, dx0;
	Matrix2d K2di, K2d;

	// zero accumulators
	for (i = 0; i < nlocal; i++) {
	itype = type[i];
	if (setflag[itype][itype]) {
	if (gradient_correction_flag) {
	K[i].setZero();
	} else {
	K[i].setIdentity();
	}
	L[i].setZero();
	F[i].setZero();
	}
	}

	// set up neighbor list variables
	inum = list->inum;
	ilist = list->ilist;
	numneigh = list->numneigh;
	firstneigh = list->firstneigh;

	for (ii = 0; ii < inum; ii++) {
	i = ilist[ii];
	itype = type[i];
	jlist = firstneigh[i];
	jnum = numneigh[i];
	irad = radius[i];
	ivol = vfrac[i];

	// initialize Eigen data structures from LAMMPS data structures
	for (idim = 0; idim < 3; idim++) {
	x0i(idim) = x0[i][idim];
	xi(idim) = x[i][idim];
	vi(idim) = v[i][idim];
	}

	for (jj = 0; jj < jnum; jj++) {
	j = jlist[jj];
	j &= NEIGHMASK;

	for (idim = 0; idim < 3; idim++) {
	x0j(idim) = x0[j][idim];
	xj(idim) = x[j][idim];
	vj(idim) = v[j][idim];
	}

	dx = xj - xi;

	rSq = dx.squaredNorm();
	h = irad + radius[j];
	if (rSq < h * h) {

	r = sqrt(rSq);
	jvol = vfrac[j];

	// distance vectors in current and reference configuration, velocity difference
	dv = vj - vi;
	dx0 = x0j - x0i;

	// kernel and derivative
	spiky_kernel_and_derivative(h, r, domain->dimension, wf, wfd);
	//barbara_kernel_and_derivative(h, r, domain->dimension, wf, wfd);

	// uncorrected kernel gradient
	g = (wfd / r) * dx;

	/* build correction matrix for kernel derivatives */
	if (gradient_correction_flag) {
	Ktmp = -g * dx.transpose();
	K[i] += jvol * Ktmp;
	}

	// velocity gradient L
	Ltmp = -dv * g.transpose();
	L[i] += jvol * Ltmp;

	// deformation gradient F in Eulerian frame
	du = dx - dx0;
	Ftmp = dv * g.transpose();
	F[i] += jvol * Ftmp;

	if (j < nlocal) {

	if (gradient_correction_flag) {
	K[j] += ivol * Ktmp;
	}

	L[j] += ivol * Ltmp;
	F[j] += ivol * Ftmp;
	}
	} // end if check distance
	} // end loop over j
	} // end loop over i

	/*
	* invert shape matrix and compute corrected quantities
	*/

	for (i = 0; i < nlocal; i++) {
	itype = type[i];
	if (setflag[itype][itype]) {
	if (gradient_correction_flag) {
	pseudo_inverse_SVD(K[i]);
	K[i] = LimitEigenvalues(K[i], 2.0);
	L[i] *= K[i];
	F[i] *= K[i];
	} // end if (gradient_correction[itype]) {

	/*
	* accumulate strain increments
	* we abuse the atom array "atom_data_9" for this purpose, which was originally designed to hold the deformation gradient.
	*/
	D = update->dt * 0.5 * (L[i] + L[i].transpose());
	atom_data9[i][0] += D(0, 0); // xx
	atom_data9[i][1] += D(1, 1); // yy
	atom_data9[i][2] += D(2, 2); // zz
	atom_data9[i][3] += D(0, 1); // xy
	atom_data9[i][4] += D(0, 2); // xz
	atom_data9[i][5] += D(1, 2); // yz

	} // end if (setflag[itype][itype])
	} // end loop over i = 0 to nlocal

	}

	/* ---------------------------------------------------------------------- */

	void PairULSPH::compute(int eflag, int vflag) {
	double **x = atom->x;
	double **v = atom->vest;
	double **vint = atom->v; // Velocity-Verlet algorithm velocities
	double **f = atom->f;
	double *vfrac = atom->vfrac;
	double *de = atom->de;
	double *rmass = atom->rmass;
	double *radius = atom->radius;
	double *contact_radius = atom->contact_radius;
	double **atom_data9 = atom->smd_data_9;

	int *type = atom->type;
	int nlocal = atom->nlocal;
	int i, j, ii, jj, jnum, itype, jtype, iDim, inum;
	double r, wf, wfd, h, rSq, ivol, jvol;
	double mu_ij, c_ij, rho_ij;
	double delVdotDelR, visc_magnitude, deltaE;
	int ilist, jlist, *numneigh;
	int **firstneigh;
	Vector3d fi, fj, dx, dv, f_stress, g, vinti, vintj, dvint;
	Vector3d xi, xj, vi, vj, f_visc, sumForces, f_stress_new;
	Vector3d gamma, f_hg, dx0, du_est, du;
	double r_ref, weight, p;
	//int periodic = (domain->xperiodic \|\| domain->yperiodic \|\| domain->zperiodic);

	double ini_dist;
	Matrix3d S, D, V, eye;
	eye.setIdentity();
	int k;
	SelfAdjointEigenSolver < Matrix3d > es;

	if (eflag \|\| vflag)
	ev_setup(eflag, vflag);
	else
	evflag = vflag_fdotr = 0;

	if (atom->nmax > nmax) {
	//printf("... allocating in compute with nmax = %d\n", atom->nmax);
	nmax = atom->nmax;
	delete[] K;
	K = new Matrix3d[nmax];
	delete[] shepardWeight;
	shepardWeight = new double[nmax];
	delete[] c0;
	c0 = new double[nmax];
	delete[] smoothVel;
	smoothVel = new Vector3d[nmax];
	delete[] stressTensor;
	stressTensor = new Matrix3d[nmax];
	delete[] L;
	L = new Matrix3d[nmax];
	delete[] numNeighs;
	numNeighs = new int[nmax];
	delete[] F;
	F = new Matrix3d[nmax];
	delete[] rho;
	rho = new double[nmax];
	delete[] effm;
	effm = new double[nmax];
	}

	// zero accumulators
	for (i = 0; i < nlocal; i++) {
	shepardWeight[i] = 0.0;
	smoothVel[i].setZero();
	numNeighs[i] = 0;

	h = 2.0 * radius[i];
	r = 0.0;
	spiky_kernel_and_derivative(h, r, domain->dimension, wf, wfd);
	}

	/*
	* if this is the very first step, zero the array which holds the accumulated strain
	*/
	if (update->ntimestep == 0) {
	for (i = 0; i < nlocal; i++) {
	itype = type[i];
	if (setflag[itype][itype]) {
	for (j = 0; j < 9; j++) {
	atom_data9[i][j] = 0.0;
	}
	}
	}
	}

	if (density_summation) {
	//printf("dens summ\n");
	PreCompute_DensitySummation();

	for (i = 0; i < nlocal; i++) { //compute volumes from rho
	itype = type[i];
	if (setflag[itype][itype]) {
	vfrac[i] = rmass[i] / rho[i];
	}
	}

	}

	if (velocity_gradient) {
	PairULSPH::PreCompute(); // get velocity gradient and kernel gradient correction
	}

	PairULSPH::AssembleStressTensor();

	/*
	* QUANTITIES ABOVE HAVE ONLY BEEN CALCULATED FOR NLOCAL PARTICLES.
	* NEED TO DO A FORWARD COMMUNICATION TO GHOST ATOMS NOW
	*/
	comm->forward_comm_pair(this);

	updateFlag = 0;

	/*
	* iterate over pairs of particles i, j and assign forces using pre-computed pressure
	*/

	// set up neighbor list variables
	inum = list->inum;
	ilist = list->ilist;
	numneigh = list->numneigh;
	firstneigh = list->firstneigh;

	for (ii = 0; ii < inum; ii++) {
	i = ilist[ii];
	itype = type[i];
	jlist = firstneigh[i];
	jnum = numneigh[i];
	ivol = vfrac[i];

	// initialize Eigen data structures from LAMMPS data structures
	for (iDim = 0; iDim < 3; iDim++) {
	xi(iDim) = x[i][iDim];
	vi(iDim) = v[i][iDim];
	vinti(iDim) = vint[i][iDim];
	}

	for (jj = 0; jj < jnum; jj++) {
	j = jlist[jj];
	j &= NEIGHMASK;

	xj(0) = x[j][0];
	xj(1) = x[j][1];
	xj(2) = x[j][2];

	dx = xj - xi;
	rSq = dx.squaredNorm();
	h = radius[i] + radius[j];
	if (rSq < h * h) {

	// initialize Eigen data structures from LAMMPS data structures
	for (iDim = 0; iDim < 3; iDim++) {
	vj(iDim) = v[j][iDim];
	vintj(iDim) = vint[j][iDim];
	}

	r = sqrt(rSq);
	jtype = type[j];
	jvol = vfrac[j];

	// distance vectors in current and reference configuration, velocity difference
	dv = vj - vi;
	dvint = vintj - vinti;

	// kernel and derivative
	spiky_kernel_and_derivative(h, r, domain->dimension, wf, wfd);
	//barbara_kernel_and_derivative(h, r, domain->dimension, wf, wfd);

	// uncorrected kernel gradient
	g = (wfd / r) * dx;

	delVdotDelR = dx.dot(dv) / (r + 0.1 * h); // project relative velocity onto unit particle distance vector [m/s]

	S = stressTensor[i] + stressTensor[j];

	if (artificial_pressure[itype][jtype] > 0.0) {
	p = S.trace();
	if (p > 0.0) { // we are in tension
	r_ref = contact_radius[i] + contact_radius[j];
	weight = Kernel_Cubic_Spline(r, h) / Kernel_Cubic_Spline(r_ref, h);
	weight = pow(weight, 4.0);
	S -= artificial_pressure[itype][jtype] * weight * p * eye;
	}
	}

	/*
	* artificial stress to control tensile instability
	* Only works if particles are uniformly spaced initially.
	*/
	if (artificial_stress[itype][jtype] > 0.0) {
	ini_dist = contact_radius[i] + contact_radius[j];
	weight = Kernel_Cubic_Spline(r, h) / Kernel_Cubic_Spline(ini_dist, h);
	weight = pow(weight, 4.0);

	es.compute(S);
	D = es.eigenvalues().asDiagonal();
	for (k = 0; k < 3; k++) {
	if (D(k, k) > 0.0) {
	D(k, k) -= weight * artificial_stress[itype][jtype] * D(k, k);
	}
	}
	V = es.eigenvectors();
	S = V * D * V.inverse();
	}

	// compute forces
	f_stress = -ivol * jvol * S * g; // DO NOT TOUCH SIGN

	/*
	* artificial viscosity -- alpha is dimensionless
	* MonaghanBalsara form of the artificial viscosity
	*/

	c_ij = 0.5 * (c0[i] + c0[j]);
	LimitDoubleMagnitude(delVdotDelR, 1.1 * c_ij);

	mu_ij = h * delVdotDelR / (r + 0.1 * h); // units: [m * m/s / m = m/s]
	rho_ij = 0.5 * (rmass[i] / ivol + rmass[j] / jvol);
	visc_magnitude = 0.5 * (Q1[itype] + Q1[jtype]) * c_ij * mu_ij / rho_ij;
	f_visc = -rmass[i] * rmass[j] * visc_magnitude * g;

	if ((Lookup[HOURGLASS_CONTROL_AMPLITUDE][itype] > 0.0) && (Lookup[HOURGLASS_CONTROL_AMPLITUDE][jtype] > 0.0)) {
	f_hg = ComputeHourglassForce(i, itype, j, jtype, dv, dx, g, c_ij, mu_ij, rho_ij);

	} else {
	f_hg.setZero();
	}

	sumForces = f_stress + f_visc + f_hg;

	// energy rate -- project velocity onto force vector
	deltaE = sumForces.dot(dv);

	// apply forces to pair of particles
	f[i][0] += sumForces(0);
	f[i][1] += sumForces(1);
	f[i][2] += sumForces(2);
	de[i] += deltaE;

	// accumulate smooth velocities
	shepardWeight[i] += jvol * wf;
	smoothVel[i] += jvol * wf * dvint;
	numNeighs[i] += 1;

	if (j < nlocal) {
	f[j][0] -= sumForces(0);
	f[j][1] -= sumForces(1);
	f[j][2] -= sumForces(2);
	de[j] += deltaE;

	shepardWeight[j] += ivol * wf;
	smoothVel[j] -= ivol * wf * dvint;
	numNeighs[j] += 1;
	}

	// tally atomistic stress tensor
	if (evflag) {
	ev_tally_xyz(i, j, nlocal, 0, 0.0, 0.0, sumForces(0), sumForces(1), sumForces(2), dx(0), dx(1), dx(2));
	}
	}

	}
	}

	for (i = 0; i < nlocal; i++) {
	itype = type[i];
	if (setflag[itype][itype] == 1) {
	if (shepardWeight[i] != 0.0) {
	smoothVel[i] /= shepardWeight[i];
	} else {
	smoothVel[i].setZero();
	}
	} // end check if particle is SPH-type
	} // end loop over i = 0 to nlocal

	if (vflag_fdotr)
	virial_fdotr_compute();

	}

	/* ----------------------------------------------------------------------
	Assemble total stress tensor with pressure, material sterength, and
	viscosity contributions.
	------------------------------------------------------------------------- */
	void PairULSPH::AssembleStressTensor() {
	double *radius = atom->radius;
	double *vfrac = atom->vfrac;
	double *rmass = atom->rmass;
	double *eff_plastic_strain = atom->eff_plastic_strain;
	double **tlsph_stress = atom->smd_stress;
	double *e = atom->e;
	int *type = atom->type;
	int i, itype;
	int nlocal = atom->nlocal;
	Matrix3d D, Ddev, W, V, sigma_diag;
	Matrix3d eye, stressRate, StressRateDevJaumann;
	Matrix3d sigmaInitial_dev, d_dev, sigmaFinal_dev, stressRateDev, oldStressDeviator, newStressDeviator;
	double plastic_strain_increment, yieldStress;
	double dt = update->dt;
	double vol, newPressure;
	double G_eff = 0.0; // effective shear modulus
	double K_eff; // effective bulk modulus
	double M, p_wave_speed;
	double rho, effectiveViscosity;
	Matrix3d deltaStressDev;

	dtCFL = 1.0e22;
	eye.setIdentity();

	for (i = 0; i < nlocal; i++) {
	itype = type[i];
	if (setflag[itype][itype] == 1) {
	newStressDeviator.setZero();
	newPressure = 0.0;
	stressTensor[i].setZero();
	vol = vfrac[i];
	rho = rmass[i] / vfrac[i];
	effectiveViscosity = 0.0;
	K_eff = 0.0;
	G_eff = 0.0;

	//printf("rho = %f\n", rho);

	switch (eos[itype]) {
	default:
	error->one(FLERR, "unknown EOS.");
	break;
	case NONE:
	c0[i] = 1.0;
	break;
	case EOS_TAIT:
	TaitEOS_density(Lookup[EOS_TAIT_EXPONENT][itype], Lookup[REFERENCE_SOUNDSPEED][itype],
	Lookup[REFERENCE_DENSITY][itype], rho, newPressure, c0[i]);
	//printf("new pressure =%f\n", newPressure);

	break;
	case EOS_PERFECT_GAS:
	PerfectGasEOS(Lookup[EOS_PERFECT_GAS_GAMMA][itype], vol, rmass[i], e[i], newPressure, c0[i]);
	break;
	case EOS_LINEAR:
	newPressure = Lookup[BULK_MODULUS][itype] * (rho / Lookup[REFERENCE_DENSITY][itype] - 1.0);
	//printf("p=%f, rho0=%f, rho=%f\n", newPressure, Lookup[REFERENCE_DENSITY][itype], rho);
	c0[i] = Lookup[REFERENCE_SOUNDSPEED][itype];
	break;
	}

	K_eff = c0[i] * c0[i] * rho; // effective bulk modulus

	/*
	* ***************************** STRENGTH MODELS **********************************************
	*/

	if (strength[itype] != NONE) {
	/*
	* initial stress state: given by the unrotateted Cauchy stress.
	* Assemble Eigen 3d matrix from stored stress state
	*/
	oldStressDeviator(0, 0) = tlsph_stress[i][0];
	oldStressDeviator(0, 1) = tlsph_stress[i][1];
	oldStressDeviator(0, 2) = tlsph_stress[i][2];
	oldStressDeviator(1, 1) = tlsph_stress[i][3];
	oldStressDeviator(1, 2) = tlsph_stress[i][4];
	oldStressDeviator(2, 2) = tlsph_stress[i][5];
	oldStressDeviator(1, 0) = oldStressDeviator(0, 1);
	oldStressDeviator(2, 0) = oldStressDeviator(0, 2);
	oldStressDeviator(2, 1) = oldStressDeviator(1, 2);

	D = 0.5 * (L[i] + L[i].transpose());
	W = 0.5 * (L[i] - L[i].transpose()); // spin tensor:: need this for Jaumann rate
	d_dev = Deviator(D);

	switch (strength[itype]) {
	default:
	error->one(FLERR, "unknown strength model.");
	break;
	case STRENGTH_LINEAR:

	// here in a version with pressure part
	// stressRateDev = Lookup[BULK_MODULUS][itype] * d_iso * eye + 2.0 * Lookup[SHEAR_MODULUS][itype] * d_dev;
	// c0[i] = Lookup[REFERENCE_SOUNDSPEED][itype];
	// newPressure = 0.0;

	// here only stress deviator
	stressRateDev = 2.0 * Lookup[SHEAR_MODULUS][itype] * d_dev;
	//cout << "stress rate deviator is " << endl << stressRateDev << endl;
	break;

	case STRENGTH_LINEAR_PLASTIC:
	yieldStress = Lookup[YIELD_STRENGTH][itype] + Lookup[HARDENING_PARAMETER][itype] * eff_plastic_strain[i];
	LinearPlasticStrength(Lookup[SHEAR_MODULUS][itype], yieldStress, oldStressDeviator, d_dev, dt,
	newStressDeviator, stressRateDev, plastic_strain_increment);
	eff_plastic_strain[i] += plastic_strain_increment;

	break;
	}

	//double m = effective_longitudinal_modulus(itype, dt, d_iso, p_rate, d_dev, stressRate_dev, damage);

	StressRateDevJaumann = stressRateDev - W * oldStressDeviator + oldStressDeviator * W;
	newStressDeviator = oldStressDeviator + dt * StressRateDevJaumann;

	tlsph_stress[i][0] = newStressDeviator(0, 0);
	tlsph_stress[i][1] = newStressDeviator(0, 1);
	tlsph_stress[i][2] = newStressDeviator(0, 2);
	tlsph_stress[i][3] = newStressDeviator(1, 1);
	tlsph_stress[i][4] = newStressDeviator(1, 2);
	tlsph_stress[i][5] = newStressDeviator(2, 2);

	// estimate effective shear modulus for time step stability
	deltaStressDev = oldStressDeviator - newStressDeviator;
	G_eff = effective_shear_modulus(d_dev, deltaStressDev, dt, itype);

	} // end if (strength[itype] != NONE)

	if (viscosity[itype] != NONE) {
	D = 0.5 * (L[i] + L[i].transpose());
	d_dev = Deviator(D);

	switch (viscosity[itype]) {
	default:
	error->one(FLERR, "unknown viscosity model.");
	break;
	case VISCOSITY_NEWTON:
	effectiveViscosity = Lookup[VISCOSITY_MU][itype];
	// double shear_rate = 2.0
	// * sqrt(d_dev(0, 1) * d_dev(0, 1) + d_dev(0, 2) * d_dev(0, 2) + d_dev(1, 2) * d_dev(1, 2)); // 3d
	//cout << "shear rate: " << shear_rate << endl;
	//effectiveViscosity = PA6_270C(shear_rate);
	//if (effectiveViscosity > 178.062e-6) {
	// printf("effective visc is %f\n", effectiveViscosity);
	//}
	newStressDeviator = 2.0 * effectiveViscosity * d_dev; // newton original
	//cout << "this is Ddev " << endl << d_dev << endl << endl;
	break;
	}
	} // end if (viscosity[itype] != NONE)

	/*
	* assemble stress Tensor from pressure and deviatoric parts
	*/

	stressTensor[i] = -newPressure * eye + newStressDeviator;

	/*
	* stable timestep based on speed-of-sound
	*/

	M = K_eff + 4.0 * G_eff / 3.0;
	p_wave_speed = sqrt(M / rho);
	effm[i] = G_eff;
	dtCFL = MIN(2 * radius[i] / p_wave_speed, dtCFL);

	/*
	* stable timestep based on viscosity
	*/
	if (viscosity[itype] != NONE) {
	dtCFL = MIN(4 * radius[i] * radius[i] * rho / effectiveViscosity, dtCFL);
	}

	/*
	* kernel gradient correction
	*/
	if (gradient_correction_flag) {
	stressTensor[i] *= K[i];
	}
	}
	// end if (setflag[itype][itype] == 1)
	} // end loop over nlocal

	//printf("stable timestep = %g\n", 0.1 * hMin * MaxBulkVelocity);
	}

	/* ----------------------------------------------------------------------
	allocate all arrays
	------------------------------------------------------------------------- */

	void PairULSPH::allocate() {

	allocated = 1;
	int n = atom->ntypes;

	memory->create(setflag, n + 1, n + 1, "pair:setflag");

	memory->create(Q1, n + 1, "pair:Q1");
	memory->create(rho0, n + 1, "pair:Q2");
	memory->create(c0_type, n + 1, "pair:c0_type");
	memory->create(eos, n + 1, "pair:eosmodel");
	memory->create(viscosity, n + 1, "pair:viscositymodel");
	memory->create(strength, n + 1, "pair:strengthmodel");

	memory->create(Lookup, MAX_KEY_VALUE, n + 1, "pair:LookupTable");

	memory->create(artificial_pressure, n + 1, n + 1, "pair:artificial_pressure");
	memory->create(artificial_stress, n + 1, n + 1, "pair:artificial_stress");
	memory->create(cutsq, n + 1, n + 1, "pair:cutsq"); // always needs to be allocated, even with granular neighborlist

	/*
	* initialize arrays to default values
	*/

	for (int i = 1; i <= n; i++) {
	for (int j = i; j <= n; j++) {
	artificial_pressure[i][j] = 0.0;
	artificial_stress[i][j] = 0.0;
	setflag[i][j] = 0;
	}
	}

	onerad_dynamic = new double[n + 1];
	onerad_frozen = new double[n + 1];
	maxrad_dynamic = new double[n + 1];
	maxrad_frozen = new double[n + 1];

	}

	/* ----------------------------------------------------------------------
	global settings
	------------------------------------------------------------------------- */

	void PairULSPH::settings(int narg, char **arg) {
	if (narg != 3) {
	printf("narg = %d\n", narg);
	error->all(FLERR, "Illegal number of arguments for pair_style ulsph");
	}

	if (comm->me == 0) {
	printf("\n>>========>>========>>========>>========>>========>>========>>========>>========\n");
	printf("... SMD / ULSPH PROPERTIES\n\n");
	}

	if (strcmp(arg[0], "*DENSITY_SUMMATION") == 0) {
	density_summation = true;
	density_continuity = false;
	if (comm->me == 0)
	printf("... density summation active\n");
	} else if (strcmp(arg[0], "*DENSITY_CONTINUITY") == 0) {
	density_continuity = true;
	density_summation = false;
	if (comm->me == 0)
	printf("... density continuity active\n");
	} else {
	error->all(FLERR,
	"Illegal settings keyword for first keyword of pair style ulsph. Must be either DENSITY_SUMMATION or DENSITY_CONTINUITY");
	}

	if (strcmp(arg[1], "*VELOCITY_GRADIENT") == 0) {
	velocity_gradient = true;
	if (comm->me == 0)
	printf("... computation of velocity gradients active\n");
	} else if (strcmp(arg[1], "*NO_VELOCITY_GRADIENT") == 0) {
	velocity_gradient = false;
	if (comm->me == 0)
	printf("... computation of velocity gradients NOT active\n");
	} else {
	error->all(FLERR,
	"Illegal settings keyword for first keyword of pair style ulsph. Must be either VELOCITY_GRADIENT or NO_VELOCITY_GRADIENT");
	}

	if (strcmp(arg[2], "*GRADIENT_CORRECTION") == 0) {
	gradient_correction_flag = true;
	if (comm->me == 0)
	printf("... first order correction of kernel gradients is active\n");
	} else if (strcmp(arg[2], "*NO_GRADIENT_CORRECTION") == 0) {
	gradient_correction_flag = false;
	if (comm->me == 0)
	printf("... first order correction of kernel gradients is NOT active\n");
	} else {
	error->all(FLERR, "Illegal settings keyword for pair style ulsph");
	}

	// error check
	//if ((gradient_correction_flag == true) && (density_summation)) {
	// error->all(FLERR, "Cannot use DENSITY_SUMMATION in combination with YES_GRADIENT_CORRECTION");
	//}

	if (comm->me == 0)
	printf(">>========>>========>>========>>========>>========>>========>>========>>========\n");

	}

	/* ----------------------------------------------------------------------
	set coeffs for one or more type pairs
	------------------------------------------------------------------------- */

	void PairULSPH::coeff(int narg, char **arg) {
	int ioffset, iarg, iNextKwd, itype, jtype;
	char str[128];
	std::string s, t;

	if (narg < 3) {
	sprintf(str, "number of arguments for pair ulsph is too small!");
	error->all(FLERR, str);
	}
	if (!allocated)
	allocate();

	/*
	* if parameters are give in i,i form, i.e., no a cross interaction, set material parameters
	*/

	if (force->inumeric(FLERR, arg[0]) == force->inumeric(FLERR, arg[1])) {

	itype = force->inumeric(FLERR, arg[0]);
	eos[itype] = viscosity[itype] = strength[itype] = NONE;

	if (comm->me == 0) {
	printf("\n>>========>>========>>========>>========>>========>>========>>========>>========\n");
	printf("...SMD / ULSPH PROPERTIES OF PARTICLE TYPE %d\n\n", itype);
	}

	/*
	* read parameters which are common -- regardless of material / eos model
	*/

	ioffset = 2;
	if (strcmp(arg[ioffset], "*COMMON") != 0) {
	sprintf(str, "common keyword missing!");
	error->all(FLERR, str);
	} else {
	}

	t = string("*");
	iNextKwd = -1;
	for (iarg = ioffset + 1; iarg < narg; iarg++) {
	s = string(arg[iarg]);
	if (s.compare(0, t.length(), t) == 0) {
	iNextKwd = iarg;
	break;
	}
	}

	//printf("keyword following *COMMON is %s\n", arg[iNextKwd]);

	if (iNextKwd < 0) {
	sprintf(str, "no KEYWORD terminates COMMON");
	error->all(FLERR, str);
	}

	if (iNextKwd - ioffset != 5 + 1) {
	sprintf(str, "expected 5 arguments following *COMMON but got %d\n", iNextKwd - ioffset - 1);
	error->all(FLERR, str);
	}

	Lookup[REFERENCE_DENSITY][itype] = force->numeric(FLERR, arg[ioffset + 1]);
	Lookup[REFERENCE_SOUNDSPEED][itype] = force->numeric(FLERR, arg[ioffset + 2]);
	Q1[itype] = force->numeric(FLERR, arg[ioffset + 3]);
	Lookup[HEAT_CAPACITY][itype] = force->numeric(FLERR, arg[ioffset + 4]);
	Lookup[HOURGLASS_CONTROL_AMPLITUDE][itype] = force->numeric(FLERR, arg[ioffset + 5]);

	Lookup[BULK_MODULUS][itype] = Lookup[REFERENCE_SOUNDSPEED][itype] * Lookup[REFERENCE_SOUNDSPEED][itype]
	* Lookup[REFERENCE_DENSITY][itype];

	if (comm->me == 0) {
	printf("material unspecific properties for SMD/ULSPH definition of particle type %d:\n", itype);
	printf(FORMAT1, "reference density", Lookup[REFERENCE_DENSITY][itype]);
	printf(FORMAT1, "reference speed of sound", Lookup[REFERENCE_SOUNDSPEED][itype]);
	printf(FORMAT1, "linear viscosity coefficient", Q1[itype]);
	printf(FORMAT1, "heat capacity [energy / (mass * temperature)]", Lookup[HEAT_CAPACITY][itype]);
	printf(FORMAT1, "bulk modulus", Lookup[BULK_MODULUS][itype]);
	printf(FORMAT1, "hourglass control amplitude", Lookup[HOURGLASS_CONTROL_AMPLITUDE][itype]);
	}

	/*
	* read following material cards
	*/

	// if (comm->me == 0) {
	// printf("next kwd is %s\n", arg[iNextKwd]);
	// }
	while (true) {
	if (strcmp(arg[iNextKwd], "*END") == 0) {
	// if (comm->me == 0) {
	// sprintf(str, "found *END");
	// error->message(FLERR, str);
	// }
	break;
	}

	ioffset = iNextKwd;
	if (strcmp(arg[ioffset], "*EOS_TAIT") == 0) {

	/*
	* Tait EOS
	*/

	eos[itype] = EOS_TAIT;
	//printf("reading *EOS_TAIT\n");

	t = string("*");
	iNextKwd = -1;
	for (iarg = ioffset + 1; iarg < narg; iarg++) {
	s = string(arg[iarg]);
	if (s.compare(0, t.length(), t) == 0) {
	iNextKwd = iarg;
	break;
	}
	}

	if (iNextKwd < 0) {
	sprintf(str, "no KEYWORD terminates EOS_TAIT");
	error->all(FLERR, str);
	}

	if (iNextKwd - ioffset != 1 + 1) {
	sprintf(str, "expected 1 arguments following *EOS_TAIT but got %d\n", iNextKwd - ioffset - 1);
	error->all(FLERR, str);
	}

	Lookup[EOS_TAIT_EXPONENT][itype] = force->numeric(FLERR, arg[ioffset + 1]);

	if (comm->me == 0) {
	printf(FORMAT2, "Tait EOS");
	printf(FORMAT1, "Exponent", Lookup[EOS_TAIT_EXPONENT][itype]);
	}
	} // end Tait EOS

	else if (strcmp(arg[ioffset], "*EOS_PERFECT_GAS") == 0) {

	/*
	* Perfect Gas EOS
	*/

	eos[itype] = EOS_PERFECT_GAS;
	//printf("reading *EOS_PERFECT_GAS\n");

	t = string("*");
	iNextKwd = -1;
	for (iarg = ioffset + 1; iarg < narg; iarg++) {
	s = string(arg[iarg]);
	if (s.compare(0, t.length(), t) == 0) {
	iNextKwd = iarg;
	break;
	}
	}

	if (iNextKwd < 0) {
	sprintf(str, "no KEYWORD terminates EOS_PERFECT_GAS");
	error->all(FLERR, str);
	}

	if (iNextKwd - ioffset != 1 + 1) {
	sprintf(str, "expected 1 arguments following *EOS_PERFECT_GAS but got %d\n", iNextKwd - ioffset - 1);
	error->all(FLERR, str);
	}

	Lookup[EOS_PERFECT_GAS_GAMMA][itype] = force->numeric(FLERR, arg[ioffset + 1]);

	if (comm->me == 0) {
	printf(FORMAT2, "Perfect Gas EOS");
	printf(FORMAT1, "Heat Capacity Ratio Gamma", Lookup[EOS_PERFECT_GAS_GAMMA][itype]);
	}
	} // end Perfect Gas EOS
	else if (strcmp(arg[ioffset], "*EOS_LINEAR") == 0) {

	/*
	* Linear EOS
	*/

	eos[itype] = EOS_LINEAR;

	t = string("*");
	iNextKwd = -1;
	for (iarg = ioffset + 1; iarg < narg; iarg++) {
	s = string(arg[iarg]);
	if (s.compare(0, t.length(), t) == 0) {
	iNextKwd = iarg;
	break;
	}
	}

	if (iNextKwd < 0) {
	sprintf(str, "no KEYWORD terminates EOS_LINEAR");
	error->all(FLERR, str);
	}

	if (iNextKwd - ioffset != 0 + 1) {
	sprintf(str, "expected 0 arguments following *EOS_LINEAR but got %d\n", iNextKwd - ioffset - 1);
	error->all(FLERR, str);
	}

	if (comm->me == 0) {
	printf(FORMAT2, "Linear EOS");
	printf(FORMAT1, "Bulk modulus", Lookup[BULK_MODULUS][itype]);
	}
	} // end Linear EOS
	else if (strcmp(arg[ioffset], "*STRENGTH_LINEAR_PLASTIC") == 0) {

	if (velocity_gradient != true) {
	error->all(FLERR, "A strength model was requested but *VELOCITY_GRADIENT is not set");
	}

	/*
	* linear elastic / ideal plastic material model with strength
	*/

	strength[itype] = STRENGTH_LINEAR_PLASTIC;
	velocity_gradient_required = true;
	//printf("reading *LINEAR_PLASTIC\n");

	t = string("*");
	iNextKwd = -1;
	for (iarg = ioffset + 1; iarg < narg; iarg++) {
	s = string(arg[iarg]);
	if (s.compare(0, t.length(), t) == 0) {
	iNextKwd = iarg;
	break;
	}
	}

	if (iNextKwd < 0) {
	sprintf(str, "no KEYWORD terminates STRENGTH_LINEAR_PLASTIC");
	error->all(FLERR, str);
	}

	if (iNextKwd - ioffset != 3 + 1) {
	sprintf(str, "expected 3 arguments following *STRENGTH_LINEAR_PLASTIC but got %d\n", iNextKwd - ioffset - 1);
	error->all(FLERR, str);
	}

	Lookup[SHEAR_MODULUS][itype] = force->numeric(FLERR, arg[ioffset + 1]);
	Lookup[YIELD_STRENGTH][itype] = force->numeric(FLERR, arg[ioffset + 2]);
	Lookup[HARDENING_PARAMETER][itype] = force->numeric(FLERR, arg[ioffset + 3]);

	if (comm->me == 0) {
	printf(FORMAT2, "linear elastic / ideal plastic material mode");
	printf(FORMAT1, "yield_strength", Lookup[YIELD_STRENGTH][itype]);
	printf(FORMAT1, "constant hardening parameter", Lookup[HARDENING_PARAMETER][itype]);
	printf(FORMAT1, "shear modulus", Lookup[SHEAR_MODULUS][itype]);
	}
	} // end *STRENGTH_LINEAR_PLASTIC
	else if (strcmp(arg[ioffset], "*STRENGTH_LINEAR") == 0) {

	if (velocity_gradient != true) {
	error->all(FLERR, "A strength model was requested but *VELOCITY_GRADIENT is not set");
	}

	/*
	* linear elastic / ideal plastic material model with strength
	*/

	strength[itype] = STRENGTH_LINEAR;
	t = string("*");
	iNextKwd = -1;
	for (iarg = ioffset + 1; iarg < narg; iarg++) {
	s = string(arg[iarg]);
	if (s.compare(0, t.length(), t) == 0) {
	iNextKwd = iarg;
	break;
	}
	}

	if (iNextKwd < 0) {
	sprintf(str, "no KEYWORD terminates STRENGTH_LINEAR");
	error->all(FLERR, str);
	}

	if (iNextKwd - ioffset != 1 + 1) {
	sprintf(str, "expected 1 arguments following *STRENGTH_LINEAR but got %d\n", iNextKwd - ioffset - 1);
	error->all(FLERR, str);
	}

	Lookup[SHEAR_MODULUS][itype] = force->numeric(FLERR, arg[ioffset + 1]);

	if (comm->me == 0) {
	printf(FORMAT2, "linear elastic strength model");
	printf(FORMAT1, "shear modulus", Lookup[SHEAR_MODULUS][itype]);
	}
	} // end *STRENGTH_LINEAR
	else if (strcmp(arg[ioffset], "*VISCOSITY_NEWTON") == 0) {

	if (velocity_gradient != true) {
	error->all(FLERR, "A viscosity model was requested but *VELOCITY_GRADIENT is not set");
	}

	/*
	* linear elastic / ideal plastic material model with strength
	*/

	viscosity[itype] = VISCOSITY_NEWTON;
	t = string("*");
	iNextKwd = -1;
	for (iarg = ioffset + 1; iarg < narg; iarg++) {
	s = string(arg[iarg]);
	if (s.compare(0, t.length(), t) == 0) {
	iNextKwd = iarg;
	break;
	}
	}

	if (iNextKwd < 0) {
	sprintf(str, "no KEYWORD terminates VISCOSITY_NEWTON");
	error->all(FLERR, str);
	}

	if (iNextKwd - ioffset != 1 + 1) {
	sprintf(str, "expected 1 arguments following *VISCOSITY_NEWTON but got %d\n", iNextKwd - ioffset - 1);
	error->all(FLERR, str);
	}

	Lookup[VISCOSITY_MU][itype] = force->numeric(FLERR, arg[ioffset + 1]);

	if (comm->me == 0) {
	printf(FORMAT2, "Newton viscosity model");
	printf(FORMAT1, "viscosity mu", Lookup[VISCOSITY_MU][itype]);
	}
	} // end *STRENGTH_VISCOSITY_NEWTON

	else if (strcmp(arg[ioffset], "*ARTIFICIAL_PRESSURE") == 0) {

	/*
	* use Monaghan's artificial pressure to prevent particle clumping
	*/

	t = string("*");
	iNextKwd = -1;
	for (iarg = ioffset + 1; iarg < narg; iarg++) {
	s = string(arg[iarg]);
	if (s.compare(0, t.length(), t) == 0) {
	iNextKwd = iarg;
	break;
	}
	}

	if (iNextKwd < 0) {
	sprintf(str, "no KEYWORD terminates ARTIFICIAL_PRESSURE");
	error->all(FLERR, str);
	}

	if (iNextKwd - ioffset != 1 + 1) {
	sprintf(str, "expected 1 arguments following *ARTIFICIAL_PRESSURE but got %d\n", iNextKwd - ioffset - 1);
	error->all(FLERR, str);
	}

	artificial_pressure[itype][itype] = force->numeric(FLERR, arg[ioffset + 1]);

	if (comm->me == 0) {
	printf(FORMAT2, "Artificial Pressure is enabled.");
	printf(FORMAT1, "Artificial Pressure amplitude", artificial_pressure[itype][itype]);
	}
	} // end *ARTIFICIAL_PRESSURE

	else if (strcmp(arg[ioffset], "*ARTIFICIAL_STRESS") == 0) {

	/*
	* use Monaghan's artificial stress to prevent particle clumping
	*/

	t = string("*");
	iNextKwd = -1;
	for (iarg = ioffset + 1; iarg < narg; iarg++) {
	s = string(arg[iarg]);
	if (s.compare(0, t.length(), t) == 0) {
	iNextKwd = iarg;
	break;
	}
	}

	if (iNextKwd < 0) {
	sprintf(str, "no KEYWORD terminates ARTIFICIAL_STRESS");
	error->all(FLERR, str);
	}

	if (iNextKwd - ioffset != 1 + 1) {
	sprintf(str, "expected 1 arguments following *ARTIFICIAL_STRESS but got %d\n", iNextKwd - ioffset - 1);
	error->all(FLERR, str);
	}

	artificial_stress[itype][itype] = force->numeric(FLERR, arg[ioffset + 1]);

	if (comm->me == 0) {
	printf(FORMAT2, "Artificial Stress is enabled.");
	printf(FORMAT1, "Artificial Stress amplitude", artificial_stress[itype][itype]);
	}
	} // end *ARTIFICIAL_STRESS

	else {
	sprintf(str, "unknown *KEYWORD: %s", arg[ioffset]);
	error->all(FLERR, str);
	}

	}

	/*
	* copy data which is looked up in inner pairwise loops from slow maps to fast arrays
	*/

	rho0[itype] = Lookup[REFERENCE_DENSITY][itype];
	c0_type[itype] = Lookup[REFERENCE_SOUNDSPEED][itype];
	setflag[itype][itype] = 1;

	/*
	* error checks
	*/

	if ((viscosity[itype] != NONE) && (strength[itype] != NONE)) {
	sprintf(str, "cannot have both a strength and viscosity model for particle type %d", itype);
	error->all(FLERR, str);
	}

	if (eos[itype] == NONE) {
	sprintf(str, "must specify an EOS for particle type %d", itype);
	error->all(FLERR, str);
	}

	} else {
	/*
	* we are reading a cross-interaction line for particle types i, j
	*/

	itype = force->inumeric(FLERR, arg[0]);
	jtype = force->inumeric(FLERR, arg[1]);

	if (strcmp(arg[2], "*CROSS") != 0) {
	sprintf(str, "ulsph cross interaction between particle type %d and %d requested, however, *CROSS keyword is missing",
	itype, jtype);
	error->all(FLERR, str);
	}

	if (setflag[itype][itype] != 1) {
	sprintf(str,
	"ulsph cross interaction between particle type %d and %d requested, however, properties of type %d have not yet been specified",
	itype, jtype, itype);
	error->all(FLERR, str);
	}

	if (setflag[jtype][jtype] != 1) {
	sprintf(str,
	"ulsph cross interaction between particle type %d and %d requested, however, properties of type %d have not yet been specified",
	itype, jtype, jtype);
	error->all(FLERR, str);
	}

	setflag[itype][jtype] = 1;
	setflag[jtype][itype] = 1;

	if ((artificial_pressure[itype][itype] > 0.0) && (artificial_pressure[jtype][jtype] > 0.0)) {
	artificial_pressure[itype][jtype] = 0.5 * (artificial_pressure[itype][itype] + artificial_pressure[jtype][jtype]);
	artificial_pressure[jtype][itype] = artificial_pressure[itype][jtype];
	} else {
	artificial_pressure[itype][jtype] = artificial_pressure[jtype][itype] = 0.0;
	}

	if ((artificial_stress[itype][itype] > 0.0) && (artificial_stress[jtype][jtype] > 0.0)) {
	artificial_stress[itype][jtype] = 0.5 * (artificial_stress[itype][itype] + artificial_stress[jtype][jtype]);
	artificial_stress[jtype][itype] = artificial_stress[itype][jtype];
	} else {
	artificial_stress[itype][jtype] = artificial_stress[jtype][itype] = 0.0;
	}

	if (comm->me == 0) {
	printf(">>========>>========>>========>>========>>========>>========>>========>>========\n");
	}

	}
	}

	/* ----------------------------------------------------------------------
	init for one type pair i,j and corresponding j,i
	------------------------------------------------------------------------- */

	double PairULSPH::init_one(int i, int j) {

	if (!allocated)
	allocate();

	if (setflag[i][j] == 0)
	error->all(FLERR, "All pair coeffs are not set");

	// cutoff = sum of max I,J radii for
	// dynamic/dynamic & dynamic/frozen interactions, but not frozen/frozen

	double cutoff = maxrad_dynamic[i] + maxrad_dynamic[j];
	cutoff = MAX(cutoff, maxrad_frozen[i] + maxrad_dynamic[j]);
	cutoff = MAX(cutoff, maxrad_dynamic[i] + maxrad_frozen[j]);
	//printf("cutoff for pair sph/fluid = %f\n", cutoff);
	return cutoff;
	}

	/* ----------------------------------------------------------------------
	init specific to this pair style
	------------------------------------------------------------------------- */

	void PairULSPH::init_style() {
	int i;

	//printf(" in init style\n");
	// request a granular neighbor list
	int irequest = neighbor->request(this);
	neighbor->requests[irequest]->half = 0;
	neighbor->requests[irequest]->gran = 1;

	// set maxrad_dynamic and maxrad_frozen for each type
	// include future Fix pour particles as dynamic

	for (i = 1; i <= atom->ntypes; i++)
	onerad_dynamic[i] = onerad_frozen[i] = 0.0;

	double *radius = atom->radius;
	int *type = atom->type;
	int nlocal = atom->nlocal;

	for (i = 0; i < nlocal; i++)
	onerad_dynamic[type[i]] = MAX(onerad_dynamic[type[i]], radius[i]);

	MPI_Allreduce(&onerad_dynamic[1], &maxrad_dynamic[1], atom->ntypes, MPI_DOUBLE, MPI_MAX, world);
	MPI_Allreduce(&onerad_frozen[1], &maxrad_frozen[1], atom->ntypes, MPI_DOUBLE, MPI_MAX, world);

	}

	/* ----------------------------------------------------------------------
	neighbor callback to inform pair style of neighbor list to use
	optional granular history list
	------------------------------------------------------------------------- */

	void PairULSPH::init_list(int id, NeighList *ptr) {
	if (id == 0)
	list = ptr;
	}

	/* ----------------------------------------------------------------------
	memory usage of local atom-based arrays
	------------------------------------------------------------------------- */

	double PairULSPH::memory_usage() {

	//printf("in memory usage\n");

	return 11 * nmax * sizeof(double);

	}

	/* ---------------------------------------------------------------------- */

	int PairULSPH::pack_forward_comm(int n, int list, double buf, int pbc_flag, int *pbc) {
	double *vfrac = atom->vfrac;
	double *eff_plastic_strain = atom->eff_plastic_strain;
	int i, j, m;

	//printf("packing comm\n");
	m = 0;
	for (i = 0; i < n; i++) {
	j = list[i];
	buf[m++] = vfrac[j];
	buf[m++] = c0[j]; //2

	buf[m++] = stressTensor[j](0, 0); // pack symmetric stress tensor
	buf[m++] = stressTensor[j](1, 1);
	buf[m++] = stressTensor[j](2, 2);
	buf[m++] = stressTensor[j](0, 1);
	buf[m++] = stressTensor[j](0, 2);
	buf[m++] = stressTensor[j](1, 2); // 2 + 6 = 8

	buf[m++] = F[j](0, 0); // F is not symmetric
	buf[m++] = F[j](0, 1);
	buf[m++] = F[j](0, 2);
	buf[m++] = F[j](1, 0);
	buf[m++] = F[j](1, 1);
	buf[m++] = F[j](1, 2);
	buf[m++] = F[j](2, 0);
	buf[m++] = F[j](2, 1);
	buf[m++] = F[j](2, 2); // 8 + 9 = 17

	buf[m++] = eff_plastic_strain[j]; // 18
	}
	return m;
	}

	/* ---------------------------------------------------------------------- */

	void PairULSPH::unpack_forward_comm(int n, int first, double *buf) {
	double *vfrac = atom->vfrac;
	double *eff_plastic_strain = atom->eff_plastic_strain;
	int i, m, last;

	m = 0;
	last = first + n;
	for (i = first; i < last; i++) {
	vfrac[i] = buf[m++];
	c0[i] = buf[m++]; // 2

	stressTensor[i](0, 0) = buf[m++];
	stressTensor[i](1, 1) = buf[m++];
	stressTensor[i](2, 2) = buf[m++];
	stressTensor[i](0, 1) = buf[m++];
	stressTensor[i](0, 2) = buf[m++];
	stressTensor[i](1, 2) = buf[m++]; // 2 + 6 = 8
	stressTensor[i](1, 0) = stressTensor[i](0, 1);
	stressTensor[i](2, 0) = stressTensor[i](0, 2);
	stressTensor[i](2, 1) = stressTensor[i](1, 2);

	F[i](0, 0) = buf[m++];
	F[i](0, 1) = buf[m++];
	F[i](0, 2) = buf[m++];
	F[i](1, 0) = buf[m++];
	F[i](1, 1) = buf[m++];
	F[i](1, 2) = buf[m++];
	F[i](2, 0) = buf[m++];
	F[i](2, 1) = buf[m++];
	F[i](2, 2) = buf[m++]; // 8 + 9 = 17

	eff_plastic_strain[i] = buf[m++]; // 18
	}
	}

	/*
	* EXTRACT
	*/

	void PairULSPH::extract(const char str, int &i) {
	//printf("in extract\n");
	if (strcmp(str, "smd/ulsph/smoothVel_ptr") == 0) {
	return (void *) smoothVel;
	} else if (strcmp(str, "smd/ulsph/stressTensor_ptr") == 0) {
	return (void *) stressTensor;
	} else if (strcmp(str, "smd/ulsph/velocityGradient_ptr") == 0) {
	return (void *) L;
	} else if (strcmp(str, "smd/ulsph/numNeighs_ptr") == 0) {
	return (void *) numNeighs;
	} else if (strcmp(str, "smd/ulsph/dtCFL_ptr") == 0) {
	//printf("dtcfl = %f\n", dtCFL);
	return (void *) &dtCFL;
	} else if (strcmp(str, "smd/ulsph/updateFlag_ptr") == 0) {
	return (void *) &updateFlag;
	} else if (strcmp(str, "smd/ulsph/effective_modulus_ptr") == 0) {
	return (void *) effm;
	} else if (strcmp(str, "smd/ulsph/shape_matrix_ptr") == 0) {
	return (void *) K;
	}

	return NULL;
	}

	/* ----------------------------------------------------------------------
	compute effective shear modulus by dividing rate of deviatoric stress with rate of shear deformation
	------------------------------------------------------------------------- */

	double PairULSPH::effective_shear_modulus(const Matrix3d d_dev, const Matrix3d deltaStressDev, const double dt, const int itype) {
	double G_eff; // effective shear modulus, see Pronto 2d eq. 3.4.7
	double deltaStressDevSum, shearRateSq, strain_increment;

	if (domain->dimension == 3) {
	deltaStressDevSum = deltaStressDev(0, 1) * deltaStressDev(0, 1) + deltaStressDev(0, 2) * deltaStressDev(0, 2)
	+ deltaStressDev(1, 2) * deltaStressDev(1, 2);
	shearRateSq = d_dev(0, 1) * d_dev(0, 1) + d_dev(0, 2) * d_dev(0, 2) + d_dev(1, 2) * d_dev(1, 2);
	} else {
	deltaStressDevSum = deltaStressDev(0, 1) * deltaStressDev(0, 1);
	shearRateSq = d_dev(0, 1) * d_dev(0, 1);
	}

	strain_increment = dt * dt * shearRateSq;

	if (strain_increment > 1.0e-12) {
	G_eff = 0.5 * sqrt(deltaStressDevSum / strain_increment);
	} else {
	if (strength[itype] != NONE) {
	G_eff = Lookup[SHEAR_MODULUS][itype];
	} else {
	G_eff = 0.0;
	}
	}

	return G_eff;

	}

	/* ----------------------------------------------------------------------
	hourglass force for updated Lagrangian SPH
	input: particles indices i, j, particle types ityep, jtype
	------------------------------------------------------------------------- */

	Vector3d PairULSPH::ComputeHourglassForce(const int i, const int itype, const int j, const int jtype, const Vector3d dv,
	const Vector3d xij, const Vector3d g, const double c_ij, const double mu_ij, const double rho_ij) {

	double *rmass = atom->rmass;
	Vector3d dv_est, f_hg;
	double visc_magnitude;

	dv_est = -0.5 * (F[i] + F[j]) * xij;
	double hurz = dv_est.dot(dv) / (dv_est.norm() * dv.norm() + 1.0e-16);
	if (hurz < 0.0) {

	visc_magnitude = 0.5 * (Q1[itype] + Q1[jtype]) * c_ij * mu_ij / rho_ij;
	f_hg = -rmass[i] * rmass[j] * visc_magnitude * g;
	// printf(" f_hg = %f %f %f\n", f_hg(0), f_hg(1), f_hg(2));
	// printf("\nnegative\n");
	// printf(" dv_est = %f %f %f\n", dv_est(0), dv_est(1), dv_est(2));
	// printf(" dv = %f %f %f\n", dv(0), dv(1), dv(2));
	} else {
	f_hg.setZero();
	}

	return f_hg;

	}

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