/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   https://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 author: K. Michael Salerno (NRL)
   Based on tabulated dihedral (dihedral_table.cpp) by Andrew Jewett
------------------------------------------------------------------------- */

#include "dihedral_table_cut.h"

#include "atom.h"
#include "citeme.h"
#include "comm.h"
#include "error.h"
#include "force.h"
#include "math_const.h"
#include "memory.h"
#include "neighbor.h"
#include "update.h"

#include <cmath>
#include <fstream>  // IWYU pragma: keep
#include <sstream>  // IWYU pragma: keep

using namespace LAMMPS_NS;
using namespace MathConst;

static const char cite_dihedral_tablecut[] =
  "dihedral_style  table/cut  command:\n\n"
  "@Article{Salerno17,\n"
  " author =  {K. M. Salerno and N. Bernstein},\n"
  " title =   {Persistence Length, End-to-End Distance, and Structure of Coarse-Grained Polymers},\n"
  " journal = {J.~Chem.~Theory Comput.},\n"
  " year =    2018,\n"
  " DOI = 10.1021/acs.jctc.7b01229"
  "}\n\n";

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

#define TOLERANCE 0.05
#define SMALL     0.0000001

// ------------------------------------------------------------------------
// The following auxiliary functions were left out of the
// DihedralTable class either because they require template parameters,
// or because they have nothing to do with dihedral angles.
// ------------------------------------------------------------------------

// -------------------------------------------------------------------
// ---------    The function was taken verbatim from the    ---------
// ---------    GNU Scientific Library (GSL, version 1.15)   ---------
// -------------------------------------------------------------------

/* Author: Gerard Jungman */
/* for description of method see [Engeln-Mullges + Uhlig, p. 96]
 *
 *      diag[0]  offdiag[0]             0   .....  offdiag[N-1]
 *   offdiag[0]     diag[1]    offdiag[1]   .....
 *            0  offdiag[1]       diag[2]
 *            0           0    offdiag[2]   .....
 *          ...         ...
 * offdiag[N-1]         ...
 *
 */
// -- (A non-symmetric version of this function is also available.) --

enum { //GSL status return codes.
  GSL_FAILURE  = -1,
  GSL_SUCCESS  = 0,
  GSL_ENOMEM   = 8,
  GSL_EZERODIV = 12,
  GSL_EBADLEN  = 19
};



// cyc_splintD(): Evaluate the deriviative of a cyclic spline at position x,
//           with n control points at xa[], ya[], with parameters y2a[].
//           The xa[] must be monotonically increasing and their
//           range should not exceed period (ie xa[n-1] < xa[0] + period).
//           x must lie in the range:  [(xa[n-1]-period), (xa[0]+period)]
//           "period" is typically 2*PI.
static double cyc_splintD(double const *xa,
                          double const *ya,
                          double const *y2a,
                          int n,
                          double period,
                          double x)
{
  int klo = -1;
  int khi = n; // (not n-1)
  int k;
  double xlo = xa[n-1] - period;
  double xhi = xa[0] + period;
  while (khi-klo > 1) {
    k = (khi+klo) >> 1; //(k=(khi+klo)/2)
    if (xa[k] > x) {
      khi = k;
      xhi = xa[k];
    }
    else {
      klo = k;
      xlo = xa[k];
    }
  }

  if (khi == n) khi = 0;
  if (klo ==-1) klo = n-1;

  double yhi = ya[khi];
  double ylo = ya[klo];
  double h = xhi-xlo;
  double g = yhi-ylo;
  double a = (xhi-x) / h;
  double b = (x-xlo) / h;
  // Formula below taken from equation 3.3.5 of "numerical recipes in c"
  // "yD" = the derivative of y
  double yD = g/h - ( (3.0*a*a-1.0)*y2a[klo] - (3.0*b*b-1.0)*y2a[khi] ) * h/6.0;
  // For rerefence: y = a*ylo + b*yhi +
  //                  ((a*a*a-a)*y2a[klo] + (b*b*b-b)*y2a[khi]) * (h*h)/6.0;

  return yD;

} // cyc_splintD()

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

DihedralTableCut::DihedralTableCut(LAMMPS *lmp) : DihedralTable(lmp)
{
  if (lmp->citeme) lmp->citeme->add(cite_dihedral_tablecut);
  aat_k = aat_theta0_1 = aat_theta0_2 = nullptr;
}

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

DihedralTableCut::~DihedralTableCut()
{
  memory->destroy(aat_k);
  memory->destroy(aat_theta0_1);
  memory->destroy(aat_theta0_2);
}

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

void DihedralTableCut::compute(int eflag, int vflag)
{

  int i1,i2,i3,i4,i,j,k,n,type;
  double edihedral;
  double vb1x,vb1y,vb1z,vb2x,vb2y,vb2z,vb3x,vb3y,vb3z,vb2xm,vb2ym,vb2zm;
  double fphi,fpphi;
  double r1mag2,r1,r2mag2,r2,r3mag2,r3;
  double sb1,rb1,sb2,rb2,sb3,rb3,c0,r12c1;
  double r12c2,costh12,costh13,costh23,sc1,sc2,s1,s2,c;
  double phi,sinphi,a11,a22,a33,a12,a13,a23,sx1,sx2;
  double sx12,sy1,sy2,sy12,sz1,sz2,sz12;
  double t1,t2,t3,t4;
  double da1,da2;
  double s12,sin2;
  double dcosphidr[4][3],dphidr[4][3],dthetadr[2][4][3];
  double fabcd[4][3];

  edihedral = 0.0;
  ev_init(eflag,vflag);

  double **x = atom->x;
  double **f = atom->f;
  int **dihedrallist = neighbor->dihedrallist;
  int ndihedrallist = neighbor->ndihedrallist;
  int nlocal = atom->nlocal;
  int newton_bond = force->newton_bond;

  for (n = 0; n < ndihedrallist; n++) {
    i1 = dihedrallist[n][0];
    i2 = dihedrallist[n][1];
    i3 = dihedrallist[n][2];
    i4 = dihedrallist[n][3];
    type = dihedrallist[n][4];

    // 1st bond

    vb1x = x[i1][0] - x[i2][0];
    vb1y = x[i1][1] - x[i2][1];
    vb1z = x[i1][2] - x[i2][2];

    // 2nd bond

    vb2x = x[i3][0] - x[i2][0];
    vb2y = x[i3][1] - x[i2][1];
    vb2z = x[i3][2] - x[i2][2];

    vb2xm = -vb2x;
    vb2ym = -vb2y;
    vb2zm = -vb2z;

    // 3rd bond

    vb3x = x[i4][0] - x[i3][0];
    vb3y = x[i4][1] - x[i3][1];
    vb3z = x[i4][2] - x[i3][2];

    // distances

    r1mag2 = vb1x*vb1x + vb1y*vb1y + vb1z*vb1z;
    r1 = sqrt(r1mag2);
    r2mag2 = vb2x*vb2x + vb2y*vb2y + vb2z*vb2z;
    r2 = sqrt(r2mag2);
    r3mag2 = vb3x*vb3x + vb3y*vb3y + vb3z*vb3z;
    r3 = sqrt(r3mag2);

    sb1 = 1.0/r1mag2;
    rb1 = 1.0/r1;
    sb2 = 1.0/r2mag2;
    rb2 = 1.0/r2;
    sb3 = 1.0/r3mag2;
    rb3 = 1.0/r3;

    c0 = (vb1x*vb3x + vb1y*vb3y + vb1z*vb3z) * rb1*rb3;

    // angles

    r12c1 = rb1*rb2;
    r12c2 = rb2*rb3;
    costh12 = (vb1x*vb2x + vb1y*vb2y + vb1z*vb2z) * r12c1;
    costh13 = c0;
    costh23 = (vb2xm*vb3x + vb2ym*vb3y + vb2zm*vb3z) * r12c2;

    // cos and sin of 2 angles and final c

    sin2 = MAX(1.0 - costh12*costh12,0.0);
    sc1 = sqrt(sin2);
    if (sc1 < SMALL) sc1 = SMALL;
    sc1 = 1.0/sc1;

    sin2 = MAX(1.0 - costh23*costh23,0.0);
    sc2 = sqrt(sin2);
    if (sc2 < SMALL) sc2 = SMALL;
    sc2 = 1.0/sc2;

    s1 = sc1 * sc1;
    s2 = sc2 * sc2;
    s12 = sc1 * sc2;
    c = (c0 + costh12*costh23) * s12;

    // error check

    if (c > 1.0 + TOLERANCE || c < (-1.0 - TOLERANCE)) {
      int me;
      MPI_Comm_rank(world,&me);
      if (screen) {
        char str[128];
        sprintf(str,"Dihedral problem: %d " BIGINT_FORMAT " "
                TAGINT_FORMAT " " TAGINT_FORMAT " "
                TAGINT_FORMAT " " TAGINT_FORMAT,
                me,update->ntimestep,
                atom->tag[i1],atom->tag[i2],atom->tag[i3],atom->tag[i4]);
        error->warning(FLERR,str,0);
        fprintf(screen,"  1st atom: %d %g %g %g\n",
                me,x[i1][0],x[i1][1],x[i1][2]);
        fprintf(screen,"  2nd atom: %d %g %g %g\n",
                me,x[i2][0],x[i2][1],x[i2][2]);
        fprintf(screen,"  3rd atom: %d %g %g %g\n",
                me,x[i3][0],x[i3][1],x[i3][2]);
        fprintf(screen,"  4th atom: %d %g %g %g\n",
                me,x[i4][0],x[i4][1],x[i4][2]);
      }
    }

    if (c > 1.0) c = 1.0;
    if (c < -1.0) c = -1.0;
    double phil = acos(c);
    phi = acos(c);

    sinphi = sqrt(1.0 - c*c);
    sinphi = MAX(sinphi,SMALL);

    // n123 = vb1 x vb2

    double n123x = vb1y*vb2z - vb1z*vb2y;
    double n123y = vb1z*vb2x - vb1x*vb2z;
    double n123z = vb1x*vb2y - vb1y*vb2x;
    double n123_dot_vb3 = n123x*vb3x + n123y*vb3y + n123z*vb3z;
    if (n123_dot_vb3 > 0.0) {
      phil = -phil;
      phi = -phi;
      sinphi = -sinphi;
    }

    a11 = -c*sb1*s1;
    a22 = sb2 * (2.0*costh13*s12 - c*(s1+s2));
    a33 = -c*sb3*s2;
    a12 = r12c1 * (costh12*c*s1 + costh23*s12);
    a13 = rb1*rb3*s12;
    a23 = r12c2 * (-costh23*c*s2 - costh12*s12);

    sx1  = a11*vb1x + a12*vb2x + a13*vb3x;
    sx2  = a12*vb1x + a22*vb2x + a23*vb3x;
    sx12 = a13*vb1x + a23*vb2x + a33*vb3x;
    sy1  = a11*vb1y + a12*vb2y + a13*vb3y;
    sy2  = a12*vb1y + a22*vb2y + a23*vb3y;
    sy12 = a13*vb1y + a23*vb2y + a33*vb3y;
    sz1  = a11*vb1z + a12*vb2z + a13*vb3z;
    sz2  = a12*vb1z + a22*vb2z + a23*vb3z;
    sz12 = a13*vb1z + a23*vb2z + a33*vb3z;

    // set up d(cos(phi))/d(r) and dphi/dr arrays

    dcosphidr[0][0] = -sx1;
    dcosphidr[0][1] = -sy1;
    dcosphidr[0][2] = -sz1;
    dcosphidr[1][0] = sx2 + sx1;
    dcosphidr[1][1] = sy2 + sy1;
    dcosphidr[1][2] = sz2 + sz1;
    dcosphidr[2][0] = sx12 - sx2;
    dcosphidr[2][1] = sy12 - sy2;
    dcosphidr[2][2] = sz12 - sz2;
    dcosphidr[3][0] = -sx12;
    dcosphidr[3][1] = -sy12;
    dcosphidr[3][2] = -sz12;

    for (i = 0; i < 4; i++)
      for (j = 0; j < 3; j++)
        dphidr[i][j] = -dcosphidr[i][j] / sinphi;


    for (i = 0; i < 4; i++)
      for (j = 0; j < 3; j++)
        fabcd[i][j] = 0;
    edihedral = 0;


    // set up d(theta)/d(r) array
    // dthetadr(i,j,k) = angle i, atom j, coordinate k

    for (i = 0; i < 2; i++)
      for (j = 0; j < 4; j++)
        for (k = 0; k < 3; k++)
          dthetadr[i][j][k] = 0.0;

    t1 = costh12 / r1mag2;
    t2 = costh23 / r2mag2;
    t3 = costh12 / r2mag2;
    t4 = costh23 / r3mag2;

    // angle12

    dthetadr[0][0][0] = sc1 * ((t1 * vb1x) - (vb2x * r12c1));
    dthetadr[0][0][1] = sc1 * ((t1 * vb1y) - (vb2y * r12c1));
    dthetadr[0][0][2] = sc1 * ((t1 * vb1z) - (vb2z * r12c1));

    dthetadr[0][1][0] = sc1 * ((-t1 * vb1x) + (vb2x * r12c1) +
                               (-t3 * vb2x) + (vb1x * r12c1));
    dthetadr[0][1][1] = sc1 * ((-t1 * vb1y) + (vb2y * r12c1) +
                               (-t3 * vb2y) + (vb1y * r12c1));
    dthetadr[0][1][2] = sc1 * ((-t1 * vb1z) + (vb2z * r12c1) +
                               (-t3 * vb2z) + (vb1z * r12c1));

    dthetadr[0][2][0] = sc1 * ((t3 * vb2x) - (vb1x * r12c1));
    dthetadr[0][2][1] = sc1 * ((t3 * vb2y) - (vb1y * r12c1));
    dthetadr[0][2][2] = sc1 * ((t3 * vb2z) - (vb1z * r12c1));

    // angle23

    dthetadr[1][1][0] = sc2 * ((t2 * vb2x) + (vb3x * r12c2));
    dthetadr[1][1][1] = sc2 * ((t2 * vb2y) + (vb3y * r12c2));
    dthetadr[1][1][2] = sc2 * ((t2 * vb2z) + (vb3z * r12c2));

    dthetadr[1][2][0] = sc2 * ((-t2 * vb2x) - (vb3x * r12c2) +
                               (t4 * vb3x) + (vb2x * r12c2));
    dthetadr[1][2][1] = sc2 * ((-t2 * vb2y) - (vb3y * r12c2) +
                               (t4 * vb3y) + (vb2y * r12c2));
    dthetadr[1][2][2] = sc2 * ((-t2 * vb2z) - (vb3z * r12c2) +
                               (t4 * vb3z) + (vb2z * r12c2));

    dthetadr[1][3][0] = -sc2 * ((t4 * vb3x) + (vb2x * r12c2));
    dthetadr[1][3][1] = -sc2 * ((t4 * vb3y) + (vb2y * r12c2));
    dthetadr[1][3][2] = -sc2 * ((t4 * vb3z) + (vb2z * r12c2));

    // angle/angle/torsion cutoff

    da1 = acos(costh12) - aat_theta0_1[type] ;
    da2 = acos(costh23) - aat_theta0_1[type] ;
    double dtheta = aat_theta0_2[type]-aat_theta0_1[type];

    fphi = 0.0;
    fpphi = 0.0;
    if (phil < 0) phil +=MY_2PI;
    uf_lookup(type, phil, fphi, fpphi);

    double gt = aat_k[type];
    double gtt = aat_k[type];
    double gpt = 0;
    double gptt = 0;

    if ( acos(costh12) > aat_theta0_1[type]) {
      gt *= 1-da1*da1/dtheta/dtheta;
      gpt = -aat_k[type]*2*da1/dtheta/dtheta;
    }

    if ( acos(costh23) > aat_theta0_1[type]) {
      gtt *= 1-da2*da2/dtheta/dtheta;
      gptt = -aat_k[type]*2*da2/dtheta/dtheta;
    }

    if (eflag) edihedral = gt*gtt*fphi;

      for (i = 0; i < 4; i++)
        for (j = 0; j < 3; j++)
          fabcd[i][j] -=  gt*gtt*fpphi*dphidr[i][j]
            - gt*gptt*fphi*dthetadr[1][i][j] + gpt*gtt*fphi*dthetadr[0][i][j];

    // apply force to each of 4 atoms

    if (newton_bond || i1 < nlocal) {
      f[i1][0] += fabcd[0][0];
      f[i1][1] += fabcd[0][1];
      f[i1][2] += fabcd[0][2];
    }

    if (newton_bond || i2 < nlocal) {
      f[i2][0] += fabcd[1][0];
      f[i2][1] += fabcd[1][1];
      f[i2][2] += fabcd[1][2];
    }

    if (newton_bond || i3 < nlocal) {
      f[i3][0] += fabcd[2][0];
      f[i3][1] += fabcd[2][1];
      f[i3][2] += fabcd[2][2];
    }

    if (newton_bond || i4 < nlocal) {
      f[i4][0] += fabcd[3][0];
      f[i4][1] += fabcd[3][1];
      f[i4][2] += fabcd[3][2];
    }

    if (evflag)
      ev_tally(i1,i2,i3,i4,nlocal,newton_bond,edihedral,
               fabcd[0],fabcd[2],fabcd[3],
               vb1x,vb1y,vb1z,vb2x,vb2y,vb2z,vb3x,vb3y,vb3z);
  }
}

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

void DihedralTableCut::allocate()
{
  allocated = 1;
  int n = atom->ndihedraltypes;

  memory->create(aat_k,n+1,"dihedral:aat_k");
  memory->create(aat_theta0_1,n+1,"dihedral:aat_theta0_1");
  memory->create(aat_theta0_2,n+1,"dihedral:aat_theta0_2");

  memory->create(tabindex,n+1,"dihedral:tabindex");
  memory->create(setflag,n+1,"dihedral:setflag");
  for (int i = 1; i <= n; i++) setflag[i] = 0;
}

/* ----------------------------------------------------------------------
   set coeffs for one or more types
   arg1 = "aat" -> AngleAngleTorsion coeffs
   arg1 -> Dihedral coeffs
------------------------------------------------------------------------- */

void DihedralTableCut::coeff(int narg, char **arg)
{
  if (narg != 7) error->all(FLERR,"Incorrect args for dihedral coefficients");
  if (!allocated) allocate();

  int ilo,ihi;
  utils::bounds(FLERR,arg[0],1,atom->ndihedraltypes,ilo,ihi,error);

  double k_one = utils::numeric(FLERR,arg[2],false,lmp);
  double theta0_1_one = utils::numeric(FLERR,arg[3],false,lmp);
  double theta0_2_one = utils::numeric(FLERR,arg[4],false,lmp);

  // convert theta0's from degrees to radians

  for (int i = ilo; i <= ihi; i++) {
    aat_k[i] = k_one;
    aat_theta0_1[i] = theta0_1_one/180.0 * MY_PI;
    aat_theta0_2[i] = theta0_2_one/180.0 * MY_PI;
  }

  int me;
  MPI_Comm_rank(world,&me);
  tables = (Table *)
    memory->srealloc(tables,(ntables+1)*sizeof(Table), "dihedral:tables");
  Table *tb = &tables[ntables];
  null_table(tb);
  if (me == 0) read_table(tb,arg[5],arg[6]);
  bcast_table(tb);

  // --- check the angle data for range errors ---
  // ---  and resolve issues with periodicity  ---

  if (tb->ninput < 2)
    error->all(FLERR,fmt::format("Invalid dihedral table length: {}",arg[5]));
  else if ((tb->ninput == 2) && (tabstyle == SPLINE))
    error->all(FLERR,fmt::format("Invalid dihedral spline table length: {} "
                                 "(Try linear)",arg[5]));

  // check for monotonicity
  for (int i=0; i < tb->ninput-1; i++) {
    if (tb->phifile[i] >= tb->phifile[i+1]) {
      auto err_msg =fmt::format("Dihedral table values are not increasing "
                                "({}, entry {})",arg[5],i+1);
      if (i==0)
        err_msg += "\n(This is probably a mistake with your table format.)\n";
      error->all(FLERR,err_msg);
    }
  }

  // check the range of angles
  double philo = tb->phifile[0];
  double phihi = tb->phifile[tb->ninput-1];
  if (tb->use_degrees) {
    if ((phihi - philo) >= 360)
      error->all(FLERR,fmt::format("Dihedral table angle range must be < 360 "
                                   "degrees ({})",arg[5]));
  } else {
    if ((phihi - philo) >= MY_2PI)
      error->all(FLERR,fmt::format("Dihedral table angle range must be < 2*PI "
                                   "radians ({})",arg[5]));
  }

  // convert phi from degrees to radians
  if (tb->use_degrees) {
    for (int i=0; i < tb->ninput; i++) {
      tb->phifile[i] *= MY_PI/180.0;
      // I assume that if angles are in degrees, then the forces (f=dU/dphi)
      // are specified with "phi" in degrees as well.
      tb->ffile[i] *= 180.0/MY_PI;
    }
  }

  // We want all the phi dihedral angles to lie in the range from 0 to 2*PI.
  // But I don't want to restrict users to input their data in this range.
  // We also want the angles to be sorted in increasing order.
  // This messy code fixes these problems with the user's data:
  {
    double *phifile_tmp = new double [tb->ninput];  //temporary arrays
    double *ffile_tmp = new double [tb->ninput];  //used for sorting
    double *efile_tmp = new double [tb->ninput];

    // After re-imaging, does the range of angles cross the 0 or 2*PI boundary?
    // If so, find the discontinuity:
    int i_discontinuity = tb->ninput;
    for (int i=0; i < tb->ninput; i++) {
      double phi   = tb->phifile[i];
      // Add a multiple of 2*PI to phi until it lies in the range [0, 2*PI).
      phi -= MY_2PI * floor(phi/MY_2PI);
      phifile_tmp[i] = phi;
      efile_tmp[i] = tb->efile[i];
      ffile_tmp[i] = tb->ffile[i];
      if ((i>0) && (phifile_tmp[i] < phifile_tmp[i-1])) {
        //There should only be at most one discontinuity, because we have
        //insured that the data was sorted before imaging, and because the
        //range of angle values does not exceed 2*PI.
        i_discontinuity = i;
      }
    }

    int I = 0;
    for (int i = i_discontinuity; i < tb->ninput; i++) {
      tb->phifile[I] = phifile_tmp[i];
      tb->efile[I] = efile_tmp[i];
      tb->ffile[I] = ffile_tmp[i];
      I++;
    }
    for (int i = 0; i < i_discontinuity; i++) {
      tb->phifile[I] = phifile_tmp[i];
      tb->efile[I] = efile_tmp[i];
      tb->ffile[I] = ffile_tmp[i];
      I++;
    }

    // clean up temporary storage
    delete[] phifile_tmp;
    delete[] ffile_tmp;
    delete[] efile_tmp;
  }

  // spline read-in and compute r,e,f vectors within table

  spline_table(tb);
  compute_table(tb);

  // Optional: allow the user to print out the interpolated spline tables

  if (me == 0) {
    if (!checkU_fname.empty()) {
      std::ofstream checkU_file;
      checkU_file.open(checkU_fname, std::ios::out);
      for (int i=0; i < tablength; i++) {
        double phi = i*MY_2PI/tablength;
        double u = tb->e[i];
        if (tb->use_degrees)
          phi *= 180.0/MY_PI;
        checkU_file << phi << " " << u << "\n";
      }
      checkU_file.close();
    }
    if (!checkF_fname.empty()) {
      std::ofstream checkF_file;
      checkF_file.open(checkF_fname, std::ios::out);
      for (int i=0; i < tablength; i++) {
        double phi = i*MY_2PI/tablength;
        double f;
        if ((tabstyle == SPLINE) && (tb->f_unspecified)) {
          double dU_dphi =
            // (If the user did not specify the forces now, AND the user
            //  selected the "spline" option, (as opposed to "linear")
            //  THEN the tb->f array is uninitialized, so there's
            //  no point to print out the contents of the tb->f[] array.
            //  Instead, later on, we will calculate the force using the
            //  -cyc_splintD() routine to calculate the derivative of the
            //  energy spline, using the energy data (tb->e[]).
            //  To be nice and report something, I do the same thing here.)
            cyc_splintD(tb->phi, tb->e, tb->e2, tablength, MY_2PI,phi);
          f = -dU_dphi;
        } else
          // Otherwise we calculated the tb->f[] array.  Report its contents.
          f = tb->f[i];
        if (tb->use_degrees) {
          phi *= 180.0/MY_PI;
          // If the user wants degree angle units, we should convert our
          // internal force tables (in energy/radians) to (energy/degrees)
          f *= MY_PI/180.0;
        }
        checkF_file << phi << " " << f << "\n";
      }
      checkF_file.close();
    } // if (checkF_fname && (strlen(checkF_fname) != 0))
  } // if (me == 0)

  // store ptr to table in tabindex
  int count = 0;
  for (int i = ilo; i <= ihi; i++) {
    tabindex[i] = ntables;
    //phi0[i] = tb->phi0; <- equilibrium dihedral angles not supported
    setflag[i] = 1;
    count++;
  }
  ntables++;

  if (count == 0) error->all(FLERR,"Incorrect args for dihedral coefficients");
}