added Verlet scheme and NxN non-bonded functionality

[gromacs.git] / src / mdlib / shellfc.c

/*
 * 
 *                This source code is part of
 * 
 *                 G   R   O   M   A   C   S
 * 
 *          GROningen MAchine for Chemical Simulations
 * 
 * Written by David van der Spoel, Erik Lindahl, Berk Hess, and others.
 * Copyright (c) 1991-2000, University of Groningen, The Netherlands.
 * Copyright (c) 2001-2008, The GROMACS development team,
 * check out http://www.gromacs.org for more information.
 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * If you want to redistribute modifications, please consider that
 * scientific software is very special. Version control is crucial -
 * bugs must be traceable. We will be happy to consider code for
 * inclusion in the official distribution, but derived work must not
 * be called official GROMACS. Details are found in the README & COPYING
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 * 
 * To help us fund GROMACS development, we humbly ask that you cite
 * the papers on the package - you can find them in the top README file.
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 * 
 * And Hey:
 * Gallium Rubidium Oxygen Manganese Argon Carbon Silicon
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <string.h>
#include "typedefs.h"
#include "smalloc.h"
#include "gmx_fatal.h"
#include "vec.h"
#include "txtdump.h"
#include "mdrun.h"
#include "partdec.h"
#include "mdatoms.h"
#include "vsite.h"
#include "network.h"
#include "names.h"
#include "constr.h"
#include "domdec.h"
#include "partdec.h"
#include "physics.h"
#include "copyrite.h"
#include "shellfc.h"
#include "mtop_util.h"
#include "chargegroup.h"


typedef struct {
  int     nnucl;
  atom_id shell;                /* The shell id                         */
  atom_id nucl1,nucl2,nucl3;    /* The nuclei connected to the shell    */
  /* gmx_bool    bInterCG; */       /* Coupled to nuclei outside cg?        */
  real    k;                    /* force constant                       */
  real    k_1;                  /* 1 over force constant                */
  rvec    xold;
  rvec    fold;
  rvec    step;
} t_shell;

typedef struct gmx_shellfc {
  int     nshell_gl;       /* The number of shells in the system       */
  t_shell *shell_gl;       /* All the shells (for DD only)             */
  int     *shell_index_gl; /* Global shell index (for DD only)         */
  gmx_bool    bInterCG;        /* Are there inter charge-group shells?     */
  int     nshell;          /* The number of local shells               */
  t_shell *shell;          /* The local shells                         */
  int     shell_nalloc;    /* The allocation size of shell             */
  gmx_bool bPredict;       /* Predict shell positions                  */
  gmx_bool bRequireInit;   /* Require initialization of shell positions  */
  int     nflexcon;        /* The number of flexible constraints       */
  rvec    *x[2];           /* Array for iterative minimization         */
  rvec    *f[2];           /* Array for iterative minimization         */
  int     x_nalloc;        /* The allocation size of x and f           */
  rvec    *acc_dir;        /* Acceleration direction for flexcon       */
  rvec    *x_old;          /* Old coordinates for flexcon              */
  int     flex_nalloc;     /* The allocation size of acc_dir and x_old */
  rvec    *adir_xnold;     /* Work space for init_adir                 */
  rvec    *adir_xnew;      /* Work space for init_adir                 */
  int     adir_nalloc;     /* Work space for init_adir                 */
} t_gmx_shellfc;

        
static void pr_shell(FILE *fplog,int ns,t_shell s[])
{
  int i;
  
  fprintf(fplog,"SHELL DATA\n");
  fprintf(fplog,"%5s  %8s  %5s  %5s  %5s\n",
          "Shell","Force k","Nucl1","Nucl2","Nucl3");
  for(i=0; (i<ns); i++) {
    fprintf(fplog,"%5d  %8.3f  %5d",s[i].shell,1.0/s[i].k_1,s[i].nucl1);
    if (s[i].nnucl == 2)
      fprintf(fplog,"  %5d\n",s[i].nucl2);
    else if (s[i].nnucl == 3)
      fprintf(fplog,"  %5d  %5d\n",s[i].nucl2,s[i].nucl3);
    else
      fprintf(fplog,"\n");
  }
}

static void predict_shells(FILE *fplog,rvec x[],rvec v[],real dt,
                           int ns,t_shell s[],
                           real mass[],gmx_mtop_t *mtop,gmx_bool bInit)
{
  int  i,m,s1,n1,n2,n3;
  real dt_1,dt_2,dt_3,fudge,tm,m1,m2,m3;
  rvec *ptr;
  gmx_mtop_atomlookup_t alook=NULL;
  t_atom *atom;

  if (mass == NULL) {
    alook = gmx_mtop_atomlookup_init(mtop);
  }
  
  /* We introduce a fudge factor for performance reasons: with this choice
   * the initial force on the shells is about a factor of two lower than 
   * without
   */
  fudge = 1.0;
    
  if (bInit) {
    if (fplog)
      fprintf(fplog,"RELAX: Using prediction for initial shell placement\n");
    ptr  = x;
    dt_1 = 1;
  }
  else {
    ptr  = v;
    dt_1 = fudge*dt;
  }
    
  for(i=0; (i<ns); i++) {
    s1 = s[i].shell;
    if (bInit)
      clear_rvec(x[s1]);
    switch (s[i].nnucl) {
    case 1:
      n1 = s[i].nucl1;
      for(m=0; (m<DIM); m++)
        x[s1][m]+=ptr[n1][m]*dt_1;
      break;
    case 2:
      n1 = s[i].nucl1;
      n2 = s[i].nucl2;
      if (mass) {
        m1 = mass[n1];
        m2 = mass[n2];
      } else {
        /* Not the correct masses with FE, but it is just a prediction... */
        m1 = atom[n1].m;
        m2 = atom[n2].m;
      }
      tm = dt_1/(m1+m2);
      for(m=0; (m<DIM); m++)
        x[s1][m]+=(m1*ptr[n1][m]+m2*ptr[n2][m])*tm;
      break;
    case 3:
      n1 = s[i].nucl1;
      n2 = s[i].nucl2;
      n3 = s[i].nucl3;
      if (mass) {
        m1 = mass[n1];
        m2 = mass[n2];
        m3 = mass[n3];
      } else {
        /* Not the correct masses with FE, but it is just a prediction... */
        gmx_mtop_atomnr_to_atom(alook,n1,&atom);
        m1 = atom->m;
        gmx_mtop_atomnr_to_atom(alook,n2,&atom);
        m2 = atom->m;
        gmx_mtop_atomnr_to_atom(alook,n3,&atom);
        m3 = atom->m;
      }
      tm = dt_1/(m1+m2+m3);
      for(m=0; (m<DIM); m++)
        x[s1][m]+=(m1*ptr[n1][m]+m2*ptr[n2][m]+m3*ptr[n3][m])*tm;
      break;
    default:
      gmx_fatal(FARGS,"Shell %d has %d nuclei!",i,s[i].nnucl);
    }
  }

  if (mass == NULL) {
    gmx_mtop_atomlookup_destroy(alook);
  }
}

gmx_shellfc_t init_shell_flexcon(FILE *fplog,
                                 gmx_mtop_t *mtop,int nflexcon,
                                 rvec *x)
{
  struct gmx_shellfc *shfc;
  t_shell     *shell;
  int         *shell_index=NULL,*at2cg;
  t_atom      *atom;
  int         n[eptNR],ns,nshell,nsi;
  int         i,j,nmol,type,mb,mt,a_offset,cg,mol,ftype,nra;
  real        qS,alpha;
  int         aS,aN=0; /* Shell and nucleus */
  int         bondtypes[] = { F_BONDS, F_HARMONIC, F_CUBICBONDS, F_POLARIZATION, F_ANHARM_POL, F_WATER_POL };
#define NBT asize(bondtypes)
  t_iatom     *ia;
  gmx_mtop_atomloop_block_t aloopb;
  gmx_mtop_atomloop_all_t aloop;
  gmx_ffparams_t *ffparams;
  gmx_molblock_t *molb;
  gmx_moltype_t *molt;
  t_block     *cgs;

  /* Count number of shells, and find their indices */
  for(i=0; (i<eptNR); i++) {
    n[i] = 0;
  }

  aloopb = gmx_mtop_atomloop_block_init(mtop);
  while (gmx_mtop_atomloop_block_next(aloopb,&atom,&nmol)) {
    n[atom->ptype] += nmol;
  }

  if (fplog) {
    /* Print the number of each particle type */  
    for(i=0; (i<eptNR); i++) {
      if (n[i] != 0) {
        fprintf(fplog,"There are: %d %ss\n",n[i],ptype_str[i]);
      }
    }
  }

  nshell = n[eptShell];
  
  if (nshell == 0 && nflexcon == 0) {
    return NULL;
  }

  snew(shfc,1);
  shfc->nflexcon = nflexcon;

  if (nshell == 0) {
    return shfc;
  }

  /* We have shells: fill the shell data structure */

  /* Global system sized array, this should be avoided */
  snew(shell_index,mtop->natoms);

  aloop = gmx_mtop_atomloop_all_init(mtop);
  nshell = 0;
  while (gmx_mtop_atomloop_all_next(aloop,&i,&atom)) {
    if (atom->ptype == eptShell) {
      shell_index[i] = nshell++;
    }
  }

  snew(shell,nshell);
  
  /* Initiate the shell structures */    
  for(i=0; (i<nshell); i++) {
    shell[i].shell = NO_ATID;
    shell[i].nnucl = 0;
    shell[i].nucl1 = NO_ATID;
    shell[i].nucl2 = NO_ATID;
    shell[i].nucl3 = NO_ATID;
    /* shell[i].bInterCG=FALSE; */
    shell[i].k_1   = 0;
    shell[i].k     = 0;
  }

  ffparams = &mtop->ffparams;

  /* Now fill the structures */
  shfc->bInterCG = FALSE;
  ns = 0;
  a_offset = 0;
  for(mb=0; mb<mtop->nmolblock; mb++) {
    molb = &mtop->molblock[mb];
    molt = &mtop->moltype[molb->type];

    cgs = &molt->cgs;
    snew(at2cg,molt->atoms.nr);
    for(cg=0; cg<cgs->nr; cg++) {
      for(i=cgs->index[cg]; i<cgs->index[cg+1]; i++) {
        at2cg[i] = cg;
      }
    }

    atom = molt->atoms.atom;
    for(mol=0; mol<molb->nmol; mol++) {
      for(j=0; (j<NBT); j++) {
        ia = molt->ilist[bondtypes[j]].iatoms;
        for(i=0; (i<molt->ilist[bondtypes[j]].nr); ) {
          type  = ia[0];
          ftype = ffparams->functype[type];
          nra   = interaction_function[ftype].nratoms;
          
          /* Check whether we have a bond with a shell */
          aS = NO_ATID;
          
          switch (bondtypes[j]) {
          case F_BONDS:
          case F_HARMONIC:
          case F_CUBICBONDS:
          case F_POLARIZATION:
          case F_ANHARM_POL:
            if (atom[ia[1]].ptype == eptShell) {
              aS = ia[1];
              aN = ia[2];
            }
            else if (atom[ia[2]].ptype == eptShell) {
              aS = ia[2];
              aN = ia[1];
            }
            break;
          case F_WATER_POL:
            aN    = ia[4];  /* Dummy */
            aS    = ia[5];  /* Shell */
            break;
          default:
            gmx_fatal(FARGS,"Death Horror: %s, %d",__FILE__,__LINE__);
          }
          
          if (aS != NO_ATID) {    
            qS = atom[aS].q;
            
            /* Check whether one of the particles is a shell... */
            nsi = shell_index[a_offset+aS];
            if ((nsi < 0) || (nsi >= nshell))
              gmx_fatal(FARGS,"nsi is %d should be within 0 - %d. aS = %d",
                        nsi,nshell,aS);
            if (shell[nsi].shell == NO_ATID) {
              shell[nsi].shell = a_offset + aS;
              ns ++;
            }
            else if (shell[nsi].shell != a_offset+aS)
              gmx_fatal(FARGS,"Weird stuff in %s, %d",__FILE__,__LINE__);
            
            if      (shell[nsi].nucl1 == NO_ATID) {
              shell[nsi].nucl1 = a_offset + aN;
            } else if (shell[nsi].nucl2 == NO_ATID) {
              shell[nsi].nucl2 = a_offset + aN;
            } else if (shell[nsi].nucl3 == NO_ATID) {
              shell[nsi].nucl3 = a_offset + aN;
            } else {
              if (fplog)
                pr_shell(fplog,ns,shell);
              gmx_fatal(FARGS,"Can not handle more than three bonds per shell\n");
            }
            if (at2cg[aS] != at2cg[aN]) {
              /* shell[nsi].bInterCG = TRUE; */
              shfc->bInterCG = TRUE;
            }
            
            switch (bondtypes[j]) {
            case F_BONDS:
            case F_HARMONIC:
              shell[nsi].k    += ffparams->iparams[type].harmonic.krA;
              break;
            case F_CUBICBONDS:
              shell[nsi].k    += ffparams->iparams[type].cubic.kb;
              break;
            case F_POLARIZATION:
            case F_ANHARM_POL:
              if (!gmx_within_tol(qS, atom[aS].qB, GMX_REAL_EPS*10))
                gmx_fatal(FARGS,"polarize can not be used with qA(%e) != qB(%e) for atom %d of molecule block %d", qS, atom[aS].qB, aS+1, mb+1);
              shell[nsi].k    += sqr(qS)*ONE_4PI_EPS0/
                ffparams->iparams[type].polarize.alpha;
              break;
            case F_WATER_POL:
              if (!gmx_within_tol(qS, atom[aS].qB, GMX_REAL_EPS*10))
                gmx_fatal(FARGS,"water_pol can not be used with qA(%e) != qB(%e) for atom %d of molecule block %d", qS, atom[aS].qB, aS+1, mb+1);
              alpha          = (ffparams->iparams[type].wpol.al_x+
                                ffparams->iparams[type].wpol.al_y+
                                ffparams->iparams[type].wpol.al_z)/3.0;
              shell[nsi].k  += sqr(qS)*ONE_4PI_EPS0/alpha;
              break;
            default:
              gmx_fatal(FARGS,"Death Horror: %s, %d",__FILE__,__LINE__);
            }
            shell[nsi].nnucl++;
          }
          ia += nra+1;
          i  += nra+1;
        }
      }
      a_offset += molt->atoms.nr;
    }
    /* Done with this molecule type */
    sfree(at2cg);
  }
  
  /* Verify whether it's all correct */
  if (ns != nshell)
    gmx_fatal(FARGS,"Something weird with shells. They may not be bonded to something");
  
  for(i=0; (i<ns); i++)
    shell[i].k_1 = 1.0/shell[i].k;
  
  if (debug)
    pr_shell(debug,ns,shell);

  
  shfc->nshell_gl      = ns;
  shfc->shell_gl       = shell;
  shfc->shell_index_gl = shell_index;

  shfc->bPredict   = (getenv("GMX_NOPREDICT") == NULL);
  shfc->bRequireInit = FALSE;
  if (!shfc->bPredict) {
    if (fplog)
      fprintf(fplog,"\nWill never predict shell positions\n");
  } else {
    shfc->bRequireInit = (getenv("GMX_REQUIRE_SHELL_INIT") != NULL);
    if (shfc->bRequireInit && fplog)
      fprintf(fplog,"\nWill always initiate shell positions\n");
  }

  if (shfc->bPredict) {
    if (x) {
      predict_shells(fplog,x,NULL,0,shfc->nshell_gl,shfc->shell_gl,
                     NULL,mtop,TRUE);
    }

    if (shfc->bInterCG) {
      if (fplog)
        fprintf(fplog,"\nNOTE: there all shells that are connected to particles outside thier own charge group, will not predict shells positions during the run\n\n");
      shfc->bPredict = FALSE;
    }
  }

  return shfc;
}

void make_local_shells(t_commrec *cr,t_mdatoms *md,
                       struct gmx_shellfc *shfc)
{
  t_shell *shell;
  int a0,a1,*ind,nshell,i;
  gmx_domdec_t *dd=NULL;

  if (PAR(cr)) {
    if (DOMAINDECOMP(cr)) {
      dd = cr->dd;
      a0 = 0;
      a1 = dd->nat_home;
    } else {
      pd_at_range(cr,&a0,&a1);
    }
  } else {
    /* Single node: we need all shells, just copy the pointer */
    shfc->nshell = shfc->nshell_gl;
    shfc->shell  = shfc->shell_gl;
    
    return;
  }

  ind = shfc->shell_index_gl;

  nshell = 0;
  shell  = shfc->shell; 
  for(i=a0; i<a1; i++) {
    if (md->ptype[i] == eptShell) {
      if (nshell+1 > shfc->shell_nalloc) {
        shfc->shell_nalloc = over_alloc_dd(nshell+1);
        srenew(shell,shfc->shell_nalloc);
      }
      if (dd) {
        shell[nshell] = shfc->shell_gl[ind[dd->gatindex[i]]];
      } else {
        shell[nshell] = shfc->shell_gl[ind[i]];
      }
      /* With inter-cg shells we can no do shell prediction,
       * so we do not need the nuclei numbers.
       */
      if (!shfc->bInterCG) {
        shell[nshell].nucl1   = i + shell[nshell].nucl1 - shell[nshell].shell;
        if (shell[nshell].nnucl > 1)
          shell[nshell].nucl2 = i + shell[nshell].nucl2 - shell[nshell].shell;
        if (shell[nshell].nnucl > 2)
          shell[nshell].nucl3 = i + shell[nshell].nucl3 - shell[nshell].shell;
      }
      shell[nshell].shell = i;
      nshell++;
    }
  }

  shfc->nshell = nshell;
  shfc->shell  = shell;
}

static void do_1pos(rvec xnew,rvec xold,rvec f,real step)
{
  real xo,yo,zo;
  real dx,dy,dz;
  
  xo=xold[XX];
  yo=xold[YY];
  zo=xold[ZZ];

  dx=f[XX]*step;
  dy=f[YY]*step;
  dz=f[ZZ]*step;

  xnew[XX]=xo+dx;
  xnew[YY]=yo+dy;
  xnew[ZZ]=zo+dz;
}

static void do_1pos3(rvec xnew,rvec xold,rvec f,rvec step)
{
  real xo,yo,zo;
  real dx,dy,dz;
  
  xo=xold[XX];
  yo=xold[YY];
  zo=xold[ZZ];

  dx=f[XX]*step[XX];
  dy=f[YY]*step[YY];
  dz=f[ZZ]*step[ZZ];

  xnew[XX]=xo+dx;
  xnew[YY]=yo+dy;
  xnew[ZZ]=zo+dz;
}

static void directional_sd(FILE *log,rvec xold[],rvec xnew[],rvec acc_dir[],
                           int start,int homenr,real step)
{
  int  i;

  for(i=start; i<homenr; i++)
    do_1pos(xnew[i],xold[i],acc_dir[i],step);
}

static void shell_pos_sd(FILE *log,rvec xcur[],rvec xnew[],rvec f[],
                         int ns,t_shell s[],int count)
{
    const real step_scale_min = 0.8,
        step_scale_increment = 0.2,
        step_scale_max = 1.2,
        step_scale_multiple = (step_scale_max - step_scale_min) / step_scale_increment;
  int  i,shell,d;
  real dx,df,k_est;
#ifdef PRINT_STEP  
  real step_min,step_max;

  step_min = 1e30;
  step_max = 0;
#endif
  for(i=0; (i<ns); i++) {
    shell = s[i].shell;
    if (count == 1) {
      for(d=0; d<DIM; d++) {
        s[i].step[d] = s[i].k_1;
#ifdef PRINT_STEP
        step_min = min(step_min,s[i].step[d]);
        step_max = max(step_max,s[i].step[d]);
#endif
      }
    } else {
      for(d=0; d<DIM; d++) {
        dx = xcur[shell][d] - s[i].xold[d];
        df =    f[shell][d] - s[i].fold[d];
    /* -dx/df gets used to generate an interpolated value, but would
     * cause a NaN if df were binary-equal to zero. Values close to
     * zero won't cause problems (because of the min() and max()), so
     * just testing for binary inequality is OK. */
    if (0.0 != df)
    {
        k_est = -dx/df;
        /* Scale the step size by a factor interpolated from
         * step_scale_min to step_scale_max, as k_est goes from 0 to
         * step_scale_multiple * s[i].step[d] */
        s[i].step[d] =
            step_scale_min * s[i].step[d] +
            step_scale_increment * min(step_scale_multiple * s[i].step[d], max(k_est, 0));
    }
    else
    {
        /* Here 0 == df */
        if (gmx_numzero(dx)) /* 0 == dx */
        {
            /* Likely this will never happen, but if it does just
             * don't scale the step. */
        }
        else /* 0 != dx */
        {
            s[i].step[d] *= step_scale_max;
        }
    }
#ifdef PRINT_STEP
        step_min = min(step_min,s[i].step[d]);
        step_max = max(step_max,s[i].step[d]);
#endif
      }
    }
    copy_rvec(xcur[shell],s[i].xold);
    copy_rvec(f[shell],   s[i].fold);

    do_1pos3(xnew[shell],xcur[shell],f[shell],s[i].step);

    if (gmx_debug_at) {
      fprintf(debug,"shell[%d] = %d\n",i,shell);
      pr_rvec(debug,0,"fshell",f[shell],DIM,TRUE);
      pr_rvec(debug,0,"xold",xcur[shell],DIM,TRUE);
      pr_rvec(debug,0,"step",s[i].step,DIM,TRUE);
      pr_rvec(debug,0,"xnew",xnew[shell],DIM,TRUE);
    }
  }
#ifdef PRINT_STEP
  printf("step %.3e %.3e\n",step_min,step_max);
#endif
}

static void decrease_step_size(int nshell,t_shell s[])
{
  int i;
  
  for(i=0; i<nshell; i++)
    svmul(0.8,s[i].step,s[i].step);
}

static void print_epot(FILE *fp,gmx_large_int_t mdstep,int count,real epot,real df,
                       int ndir,real sf_dir)
{
  char buf[22];

  fprintf(fp,"MDStep=%5s/%2d EPot: %12.8e, rmsF: %6.2e",
          gmx_step_str(mdstep,buf),count,epot,df);
  if (ndir)
    fprintf(fp,", dir. rmsF: %6.2e\n",sqrt(sf_dir/ndir));
  else
    fprintf(fp,"\n");
}


static real rms_force(t_commrec *cr,rvec f[],int ns,t_shell s[],
                      int ndir,real *sf_dir,real *Epot)
{
  int  i,shell,ntot;
  double buf[4];

  buf[0] = *sf_dir;
  for(i=0; i<ns; i++) {
    shell = s[i].shell;
    buf[0]  += norm2(f[shell]);
  }
  ntot = ns;

  if (PAR(cr)) {
    buf[1] = ntot;
    buf[2] = *sf_dir;
    buf[3] = *Epot;
    gmx_sumd(4,buf,cr);
    ntot = (int)(buf[1] + 0.5);
    *sf_dir = buf[2];
    *Epot   = buf[3];
  }
  ntot += ndir;

  return (ntot ? sqrt(buf[0]/ntot) : 0);
}

static void check_pbc(FILE *fp,rvec x[],int shell)
{
  int m,now;
  
  now = shell-4;
  for(m=0; (m<DIM); m++)
    if (fabs(x[shell][m]-x[now][m]) > 0.3) {
      pr_rvecs(fp,0,"SHELL-X",x+now,5);
      break;
    }
}

static void dump_shells(FILE *fp,rvec x[],rvec f[],real ftol,int ns,t_shell s[])
{
  int  i,shell;
  real ft2,ff2;
  
  ft2 = sqr(ftol);
  
  for(i=0; (i<ns); i++) {
    shell = s[i].shell;
    ff2   = iprod(f[shell],f[shell]);
    if (ff2 > ft2)
      fprintf(fp,"SHELL %5d, force %10.5f  %10.5f  %10.5f, |f| %10.5f\n",
              shell,f[shell][XX],f[shell][YY],f[shell][ZZ],sqrt(ff2));
    check_pbc(fp,x,shell);
  }
}

static void init_adir(FILE *log,gmx_shellfc_t shfc,
                      gmx_constr_t constr,t_idef *idef,t_inputrec *ir,
                      t_commrec *cr,int dd_ac1,
                      gmx_large_int_t step,t_mdatoms *md,int start,int end,
                      rvec *x_old,rvec *x_init,rvec *x,
                      rvec *f,rvec *acc_dir,
                      gmx_bool bMolPBC,matrix box,
                      real *lambda,real *dvdlambda,t_nrnb *nrnb)
{
  rvec   *xnold,*xnew;
  double w_dt;
  int    gf,ga,gt;
  real   dt,scale;
  int    n,d; 
  unsigned short *ptype;
  rvec   p,dx;
  
  if (DOMAINDECOMP(cr))
    n = dd_ac1;
  else
    n = end - start;
  if (n > shfc->adir_nalloc) {
    shfc->adir_nalloc = over_alloc_dd(n);
    srenew(shfc->adir_xnold,shfc->adir_nalloc);
    srenew(shfc->adir_xnew ,shfc->adir_nalloc);
  }
  xnold = shfc->adir_xnold;
  xnew  = shfc->adir_xnew;
    
  ptype = md->ptype;

  dt = ir->delta_t;

  /* Does NOT work with freeze or acceleration groups (yet) */
  for (n=start; n<end; n++) {  
    w_dt = md->invmass[n]*dt;
    
    for (d=0; d<DIM; d++) {
      if ((ptype[n] != eptVSite) && (ptype[n] != eptShell)) {
        xnold[n-start][d] = x[n][d] - (x_init[n][d] - x_old[n][d]);
        xnew[n-start][d] = 2*x[n][d] - x_old[n][d] + f[n][d]*w_dt*dt;
      } else {
        xnold[n-start][d] = x[n][d];
        xnew[n-start][d] = x[n][d];
      }
    }
  }
  constrain(log,FALSE,FALSE,constr,idef,ir,NULL,cr,step,0,md,
            x,xnold-start,NULL,bMolPBC,box,
            lambda[efptBONDED],&(dvdlambda[efptBONDED]),
            NULL,NULL,nrnb,econqCoord,FALSE,0,0);
  constrain(log,FALSE,FALSE,constr,idef,ir,NULL,cr,step,0,md,
            x,xnew-start,NULL,bMolPBC,box,
            lambda[efptBONDED],&(dvdlambda[efptBONDED]),
            NULL,NULL,nrnb,econqCoord,FALSE,0,0);

  for (n=start; n<end; n++) {
    for(d=0; d<DIM; d++)
      xnew[n-start][d] =
        -(2*x[n][d]-xnold[n-start][d]-xnew[n-start][d])/sqr(dt)
        - f[n][d]*md->invmass[n];
    clear_rvec(acc_dir[n]);
  }

  /* Project the acceleration on the old bond directions */
  constrain(log,FALSE,FALSE,constr,idef,ir,NULL,cr,step,0,md,
            x_old,xnew-start,acc_dir,bMolPBC,box,
            lambda[efptBONDED],&(dvdlambda[efptBONDED]),
            NULL,NULL,nrnb,econqDeriv_FlexCon,FALSE,0,0); 
}

int relax_shell_flexcon(FILE *fplog,t_commrec *cr,gmx_bool bVerbose,
                        gmx_large_int_t mdstep,t_inputrec *inputrec,
                        gmx_bool bDoNS,int force_flags,
                        gmx_bool bStopCM,
                        gmx_localtop_t *top,
                        gmx_mtop_t* mtop,
                        gmx_constr_t constr,
                        gmx_enerdata_t *enerd,t_fcdata *fcd,
                        t_state *state,rvec f[],
                        tensor force_vir,
                        t_mdatoms *md,
                        t_nrnb *nrnb,gmx_wallcycle_t wcycle,
                        t_graph *graph,
                        gmx_groups_t *groups,
                        struct gmx_shellfc *shfc,
                        t_forcerec *fr,
                        gmx_bool bBornRadii,
                        double t,rvec mu_tot,
                        int natoms,gmx_bool *bConverged,
                        gmx_vsite_t *vsite,
                        FILE *fp_field)
{
  int    nshell;
  t_shell *shell;
  t_idef *idef;
  rvec   *pos[2],*force[2],*acc_dir=NULL,*x_old=NULL;
  real   Epot[2],df[2];
  rvec   dx;
  real   sf_dir,invdt;
  real   ftol,xiH,xiS,dum=0;
  char   sbuf[22];
  gmx_bool   bCont,bInit;
  int    nat,dd_ac0,dd_ac1=0,i;
  int    start=md->start,homenr=md->homenr,end=start+homenr,cg0,cg1;
  int    nflexcon,g,number_steps,d,Min=0,count=0;
#define  Try (1-Min)             /* At start Try = 1 */

  bCont        = (mdstep == inputrec->init_step) && inputrec->bContinuation;
  bInit        = (mdstep == inputrec->init_step) || shfc->bRequireInit;
  ftol         = inputrec->em_tol;
  number_steps = inputrec->niter;
  nshell       = shfc->nshell;
  shell        = shfc->shell;
  nflexcon     = shfc->nflexcon;

  idef = &top->idef;

  if (DOMAINDECOMP(cr)) {
    nat = dd_natoms_vsite(cr->dd);
    if (nflexcon > 0) {
      dd_get_constraint_range(cr->dd,&dd_ac0,&dd_ac1);
      nat = max(nat,dd_ac1);
    }
  } else {
    nat = state->natoms;
  }

  if (nat > shfc->x_nalloc) {
    /* Allocate local arrays */
    shfc->x_nalloc = over_alloc_dd(nat);
    for(i=0; (i<2); i++) {
      srenew(shfc->x[i],shfc->x_nalloc);
      srenew(shfc->f[i],shfc->x_nalloc);
    }
  }
  for(i=0; (i<2); i++) {
    pos[i]   = shfc->x[i];
    force[i] = shfc->f[i];
  }
     
  /* With particle decomposition this code only works
   * when all particles involved with each shell are in the same cg.
   */

  if (bDoNS && inputrec->ePBC != epbcNONE && !DOMAINDECOMP(cr)) {
    /* This is the only time where the coordinates are used
     * before do_force is called, which normally puts all
     * charge groups in the box.
     */
    if (PARTDECOMP(cr)) {
      pd_cg_range(cr,&cg0,&cg1);
    } else {
      cg0 = 0;
      cg1 = top->cgs.nr;
    }
    put_charge_groups_in_box(fplog,cg0,cg1,fr->ePBC,state->box,
                             &(top->cgs),state->x,fr->cg_cm);
    if (graph)
      mk_mshift(fplog,graph,fr->ePBC,state->box,state->x);
  }

  /* After this all coordinate arrays will contain whole molecules */
  if (graph)
    shift_self(graph,state->box,state->x);

  if (nflexcon) {
    if (nat > shfc->flex_nalloc) {
      shfc->flex_nalloc = over_alloc_dd(nat);
      srenew(shfc->acc_dir,shfc->flex_nalloc);
      srenew(shfc->x_old,shfc->flex_nalloc);
    }
    acc_dir = shfc->acc_dir;
    x_old   = shfc->x_old;
    for(i=0; i<homenr; i++) {
      for(d=0; d<DIM; d++)
        shfc->x_old[i][d] =
          state->x[start+i][d] - state->v[start+i][d]*inputrec->delta_t;
    }
  }

  /* Do a prediction of the shell positions */
  if (shfc->bPredict && !bCont) {
    predict_shells(fplog,state->x,state->v,inputrec->delta_t,nshell,shell,
                   md->massT,NULL,bInit);
  }

  /* do_force expected the charge groups to be in the box */
  if (graph)
    unshift_self(graph,state->box,state->x);

  /* Calculate the forces first time around */
  if (gmx_debug_at) {
    pr_rvecs(debug,0,"x b4 do_force",state->x + start,homenr);
  }
  do_force(fplog,cr,inputrec,mdstep,nrnb,wcycle,top,mtop,groups,
           state->box,state->x,&state->hist,
           force[Min],force_vir,md,enerd,fcd,
           state->lambda,graph,
           fr,vsite,mu_tot,t,fp_field,NULL,bBornRadii,
           (bDoNS ? GMX_FORCE_NS : 0) | force_flags);

  sf_dir = 0;
  if (nflexcon) {
    init_adir(fplog,shfc,
              constr,idef,inputrec,cr,dd_ac1,mdstep,md,start,end,
              shfc->x_old-start,state->x,state->x,force[Min],
              shfc->acc_dir-start,
              fr->bMolPBC,state->box,state->lambda,&dum,nrnb);

    for(i=start; i<end; i++)
      sf_dir += md->massT[i]*norm2(shfc->acc_dir[i-start]);
  }

  Epot[Min] = enerd->term[F_EPOT];

  df[Min]=rms_force(cr,shfc->f[Min],nshell,shell,nflexcon,&sf_dir,&Epot[Min]);
  df[Try]=0;
  if (debug) {
    fprintf(debug,"df = %g  %g\n",df[Min],df[Try]);
  }

  if (gmx_debug_at) {
    pr_rvecs(debug,0,"force0",force[Min],md->nr);
  }

  if (nshell+nflexcon > 0) {
    /* Copy x to pos[Min] & pos[Try]: during minimization only the
     * shell positions are updated, therefore the other particles must
     * be set here.
     */
    memcpy(pos[Min],state->x,nat*sizeof(state->x[0]));
    memcpy(pos[Try],state->x,nat*sizeof(state->x[0]));
  }
  
  if (bVerbose && MASTER(cr))
    print_epot(stdout,mdstep,0,Epot[Min],df[Min],nflexcon,sf_dir);

  if (debug) {
    fprintf(debug,"%17s: %14.10e\n",
            interaction_function[F_EKIN].longname,enerd->term[F_EKIN]);
    fprintf(debug,"%17s: %14.10e\n",
            interaction_function[F_EPOT].longname,enerd->term[F_EPOT]);
    fprintf(debug,"%17s: %14.10e\n",
            interaction_function[F_ETOT].longname,enerd->term[F_ETOT]);
    fprintf(debug,"SHELLSTEP %s\n",gmx_step_str(mdstep,sbuf));
  }
  
  /* First check whether we should do shells, or whether the force is 
   * low enough even without minimization.
   */
  *bConverged = (df[Min] < ftol);
  
  for(count=1; (!(*bConverged) && (count < number_steps)); count++) {
    if (vsite)
      construct_vsites(fplog,vsite,pos[Min],nrnb,inputrec->delta_t,state->v,
                       idef->iparams,idef->il,
                       fr->ePBC,fr->bMolPBC,graph,cr,state->box);
     
    if (nflexcon) {
      init_adir(fplog,shfc,
                constr,idef,inputrec,cr,dd_ac1,mdstep,md,start,end,
                x_old-start,state->x,pos[Min],force[Min],acc_dir-start,
                fr->bMolPBC,state->box,state->lambda,&dum,nrnb);
      
      directional_sd(fplog,pos[Min],pos[Try],acc_dir-start,start,end,
                     fr->fc_stepsize);
    }
    
    /* New positions, Steepest descent */
    shell_pos_sd(fplog,pos[Min],pos[Try],force[Min],nshell,shell,count); 

    /* do_force expected the charge groups to be in the box */
    if (graph)
      unshift_self(graph,state->box,pos[Try]);

    if (gmx_debug_at) {
      pr_rvecs(debug,0,"RELAX: pos[Min]  ",pos[Min] + start,homenr);
      pr_rvecs(debug,0,"RELAX: pos[Try]  ",pos[Try] + start,homenr);
    }
    /* Try the new positions */
    do_force(fplog,cr,inputrec,1,nrnb,wcycle,
             top,mtop,groups,state->box,pos[Try],&state->hist,
             force[Try],force_vir,
             md,enerd,fcd,state->lambda,graph,
             fr,vsite,mu_tot,t,fp_field,NULL,bBornRadii,
             force_flags);
    
    if (gmx_debug_at) {
      pr_rvecs(debug,0,"RELAX: force[Min]",force[Min] + start,homenr);
      pr_rvecs(debug,0,"RELAX: force[Try]",force[Try] + start,homenr);
    }
    sf_dir = 0;
    if (nflexcon) {
      init_adir(fplog,shfc,
                constr,idef,inputrec,cr,dd_ac1,mdstep,md,start,end,
                x_old-start,state->x,pos[Try],force[Try],acc_dir-start,
                fr->bMolPBC,state->box,state->lambda,&dum,nrnb);

      for(i=start; i<end; i++)
        sf_dir += md->massT[i]*norm2(acc_dir[i-start]);
    }

    Epot[Try] = enerd->term[F_EPOT]; 
    
    df[Try]=rms_force(cr,force[Try],nshell,shell,nflexcon,&sf_dir,&Epot[Try]);

    if (debug)
      fprintf(debug,"df = %g  %g\n",df[Min],df[Try]);

    if (debug) {
      if (gmx_debug_at)
        pr_rvecs(debug,0,"F na do_force",force[Try] + start,homenr);
      if (gmx_debug_at) {
        fprintf(debug,"SHELL ITER %d\n",count);
        dump_shells(debug,pos[Try],force[Try],ftol,nshell,shell);
      }
    }

    if (bVerbose && MASTER(cr))
      print_epot(stdout,mdstep,count,Epot[Try],df[Try],nflexcon,sf_dir);
      
    *bConverged = (df[Try] < ftol);
    
    if ((df[Try] < df[Min])) {
      if (debug)
        fprintf(debug,"Swapping Min and Try\n");
      if (nflexcon) {
        /* Correct the velocities for the flexible constraints */
        invdt = 1/inputrec->delta_t;
        for(i=start; i<end; i++) {
          for(d=0; d<DIM; d++)
            state->v[i][d] += (pos[Try][i][d] - pos[Min][i][d])*invdt;
        }
      }
      Min  = Try;
    } else {
      decrease_step_size(nshell,shell);
    }
  }
  if (MASTER(cr) && !(*bConverged)) {
    /* Note that the energies and virial are incorrect when not converged */
    if (fplog)
      fprintf(fplog,
              "step %s: EM did not converge in %d iterations, RMS force %.3f\n",
              gmx_step_str(mdstep,sbuf),number_steps,df[Min]);
    fprintf(stderr,
            "step %s: EM did not converge in %d iterations, RMS force %.3f\n",
            gmx_step_str(mdstep,sbuf),number_steps,df[Min]);
  }

  /* Copy back the coordinates and the forces */
  memcpy(state->x,pos[Min],nat*sizeof(state->x[0]));
  memcpy(f,force[Min],nat*sizeof(f[0]));

  return count; 
}