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fix_controller.cpp
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Thu, Aug 15, 17:15

fix_controller.cpp
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/* ----------------------------------------------------------------------
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 <stdlib.h>
#include <string.h>
#include "fix_controller.h"
#include "force.h"
#include "update.h"
#include "modify.h"
#include "compute.h"
#include "input.h"
#include "variable.h"
#include "error.h"
using namespace LAMMPS_NS;
using namespace FixConst;
enum{COMPUTE,FIX,VARIABLE};
#define INVOKED_SCALAR 1
#define INVOKED_VECTOR 2
/* ---------------------------------------------------------------------- */
FixController::FixController(LAMMPS *lmp, int narg, char **arg) :
Fix(lmp, narg, arg)
{
if (narg != 11) error->all(FLERR,"Illegal fix controller command");
vector_flag = 1;
size_vector = 3;
global_freq = 1;
extvector = 0;
nevery = force->inumeric(FLERR,arg[3]);
if (nevery <= 0) error->all(FLERR,"Illegal fix controller command");
alpha = force->numeric(FLERR,arg[4]);
kp = force->numeric(FLERR,arg[5]);
ki = force->numeric(FLERR,arg[6]);
kd = force->numeric(FLERR,arg[7]);
pvID = cvID = NULL;
// process variable arg
int iarg = 8;
if (strncmp(arg[iarg],"c_",2) == 0 ||
strncmp(arg[iarg],"f_",2) == 0 ||
strncmp(arg[iarg],"v_",2) == 0) {
if (arg[iarg][0] == 'c') pvwhich = COMPUTE;
else if (arg[iarg][0] == 'f') pvwhich = FIX;
else if (arg[iarg][0] == 'v') pvwhich = VARIABLE;
int n = strlen(arg[iarg]);
char *suffix = new char[n];
strcpy(suffix,&arg[iarg][2]);
char *ptr = strchr(suffix,'[');
if (ptr) {
if (suffix[strlen(suffix)-1] != ']')
error->all(FLERR,"Illegal fix controller command");
pvindex = atoi(ptr+1);
*ptr = '\0';
} else pvindex = 0;
n = strlen(suffix) + 1;
pvID = new char[n];
strcpy(pvID,suffix);
delete [] suffix;
iarg++;
} else error->all(FLERR,"Illegal fix controller command");
// setpoint arg
setpoint = force->numeric(FLERR,arg[iarg]);
iarg++;
// control variable arg
int n = strlen(arg[iarg]) + 1;
cvID = new char[n];
strcpy(cvID,arg[iarg]);
// error check
if (pvwhich == COMPUTE) {
int icompute = modify->find_compute(pvID);
if (icompute < 0)
error->all(FLERR,"Compute ID for fix controller does not exist");
Compute *c = modify->compute[icompute];
int flag = 0;
if (c->scalar_flag && pvindex == 0) flag = 1;
else if (c->vector_flag && pvindex > 0) flag = 1;
if (!flag) error->all(FLERR,"Fix controller compute does not "
"calculate a global scalar or vector");
if (pvindex && pvindex > c->size_vector)
error->all(FLERR,"Fix controller compute vector is "
"accessed out-of-range");
} else if (pvwhich == FIX) {
int ifix = modify->find_fix(pvID);
if (ifix < 0)
error->all(FLERR,"Fix ID for fix controller does not exist");
Fix *f = modify->fix[ifix];
int flag = 0;
if (f->scalar_flag && pvindex == 0) flag = 1;
else if (f->vector_flag && pvindex > 0) flag = 1;
if (!flag) error->all(FLERR,"Fix controller fix does not "
"calculate a global scalar or vector");
if (pvindex && pvindex > f->size_vector)
error->all(FLERR,"Fix controller fix vector is accessed out-of-range");
} else if (pvwhich == FIX) {
int ivariable = input->variable->find(pvID);
if (ivariable < 0)
error->all(FLERR,"Variable name for fix controller does not exist");
if (input->variable->equalstyle(ivariable) == 0)
error->all(FLERR,"Fix controller variable is not equal-style variable");
}
int ivariable = input->variable->find(cvID);
if (ivariable < 0)
error->all(FLERR,"Variable name for fix controller does not exist");
if (input->variable->internalstyle(ivariable) == 0)
error->all(FLERR,"Fix controller variable is not internal-style variable");
control = input->variable->compute_equal(ivariable);
firsttime = 1;
}
/* ---------------------------------------------------------------------- */
FixController::~FixController()
{
delete [] pvID;
delete [] cvID;
}
/* ---------------------------------------------------------------------- */
int FixController::setmask()
{
int mask = 0;
mask |= END_OF_STEP;
return mask;
}
/* ---------------------------------------------------------------------- */
void FixController::init()
{
if (pvwhich == COMPUTE) {
int icompute = modify->find_compute(pvID);
if (icompute < 0)
error->all(FLERR,"Compute ID for fix controller does not exist");
pcompute = modify->compute[icompute];
} else if (pvwhich == FIX) {
int ifix = modify->find_fix(pvID);
if (ifix < 0) error->all(FLERR,"Fix ID for fix controller does not exist");
pfix = modify->fix[ifix];
} else if (pvwhich == VARIABLE) {
pvar = input->variable->find(pvID);
if (pvar < 0)
error->all(FLERR,"Variable name for fix controller does not exist");
}
cvar = input->variable->find(cvID);
if (cvar < 0)
error->all(FLERR,"Variable name for fix controller does not exist");
// set sampling time
tau = nevery * update->dt;
}
/* ---------------------------------------------------------------------- */
void FixController::end_of_step()
{
// current value of pv = invocation of compute,fix,variable
// compute/fix/variable may invoke computes so wrap with clear/add
modify->clearstep_compute();
// invoke compute if not previously invoked
double current = 0.0;
if (pvwhich == COMPUTE) {
if (pvindex == 0) {
if (!(pcompute->invoked_flag & INVOKED_SCALAR)) {
pcompute->compute_scalar();
pcompute->invoked_flag |= INVOKED_SCALAR;
}
current = pcompute->scalar;
} else {
if (!(pcompute->invoked_flag & INVOKED_VECTOR)) {
pcompute->compute_vector();
pcompute->invoked_flag |= INVOKED_VECTOR;
}
current = pcompute->vector[pvindex-1];
}
// access fix field, guaranteed to be ready
} else if (pvwhich == FIX) {
if (pvindex == 0) current = pfix->compute_scalar();
else current = pfix->compute_vector(pvindex-1);
// evaluate equal-style variable
} else if (pvwhich == VARIABLE) {
current = input->variable->compute_equal(pvar);
}
modify->addstep_compute(update->ntimestep + nevery);
// new control var = f(old value, current process var, setpoint)
// cv = cvold -kp*err -ki*sumerr -kd*deltaerr
// note: this deviates from standard notation, which is
// cv = kp*err +ki*sumerr +kd*deltaerr
// the difference is in the sign and the time integral
err = current - setpoint;
if (firsttime) {
firsttime = 0;
deltaerr = sumerr = 0.0;
} else {
deltaerr = err - olderr;
sumerr += err;
}
// 3 terms of PID equation
control += -kp * alpha * tau * err;
control += -ki * alpha * tau * tau * sumerr;
control += -kd * alpha * deltaerr;
olderr = err;
// reset control variable
input->variable->internal_set(cvar,control);
}
/* ---------------------------------------------------------------------- */
void FixController::reset_dt()
{
tau = nevery * update->dt;
}
/* ----------------------------------------------------------------------
return 3 terms of PID controller at last invocation of end_of_step()
------------------------------------------------------------------------- */
double FixController::compute_vector(int n)
{
if (n == 0) return (-kp * alpha * tau * err);
else if (n == 1) return (-ki * alpha * tau * tau * sumerr);
else return (-kd * alpha * deltaerr);
}

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