rpc/fts/brownian/LMBdStep.tpp

#ifndef RPC_LM_BD_STEP_TPP
#define RPC_LM_BD_STEP_TPP
 
/*
* PSCF - Polymer Self-Consistent Field
*
* Copyright 2015 - 2025, The Regents of the University of Minnesota
* Distributed under the terms of the GNU General Public License.
*/
 
#include "LMBdStep.h"
 
#include <rpc/fts/brownian/BdSimulator.h>
#include <rpc/fts/compressor/Compressor.h>
#include <rpc/system/System.h>
#include <rpc/solvers/Mixture.h>
#include <rpc/field/Domain.h>
#include <pscf/math/IntVec.h>
#include <util/random/Random.h>
 
namespace Pscf {
namespace Rpc {
 
   using namespace Util;
   using namespace Prdc::Cpu;
 
   /*
   * Constructor.
   */
   template <int D>
   LMBdStep<D>::LMBdStep(BdSimulator<D>& simulator)
    : BdStep<D>(simulator),
      w_(),
      etaA_(),
      etaB_(),
      dwc_(),
      etaNewPtr_(0),
      etaOldPtr_(0),
      mobility_(0.0)
   {}
 
   /*
   * Destructor, empty default implementation.
   */
   template <int D>
   LMBdStep<D>::~LMBdStep()
   {}
 
   /*
   * ReadParameters, empty default implementation.
   */
   template <int D>
   void LMBdStep<D>::readParameters(std::istream &in)
   {
      read(in, "mobility", mobility_);
 
      int nMonomer = system().mixture().nMonomer();
      IntVec<D> meshDimensions = system().domain().mesh().dimensions();
 
      // Allocate memory for private containers
      w_.allocate(nMonomer);
      for (int i=0; i < nMonomer; ++i) {
         w_[i].allocate(meshDimensions);
      }
      etaA_.allocate(nMonomer-1);
      etaB_.allocate(nMonomer-1);
      for (int i=0; i < nMonomer - 1; ++i) {
         etaA_[i].allocate(meshDimensions);
         etaB_[i].allocate(meshDimensions);
      }
      dwc_.allocate(meshDimensions);
   }
 
   /*
   * Generate new random displacement values
   */
   template <int D>
   void LMBdStep<D>::generateEtaNew()
   {
      const int nMonomer = system().mixture().nMonomer();
      const int meshSize = system().domain().mesh().size();
 
      // Prefactor b for displacements
      const double vSystem = system().domain().unitCell().volume();
      const double b = sqrt(0.5*mobility_*double(meshSize)/vSystem);
 
      int j, k;
      for (j = 0; j < nMonomer - 1; ++j) {
         RField<D>& eta = etaNew(j);
         for (k = 0; k < meshSize; ++k) {
            eta[k] = b*random().gaussian();
         }
      }
   }
 
   /*
   * Exchange pointers to old and new random fields.
   */
   template <int D>
   void LMBdStep<D>::exchangeOldNew()
   {
      DArray< RField<D> >* temp;
      temp = etaOldPtr_;
      etaOldPtr_ = etaNewPtr_;
      etaNewPtr_ = temp;
   }
 
   /*
   * Initial setup of stepper before main simulation loop.
   */
   template <int D>
   void LMBdStep<D>::setup()
   {
      int nMonomer = system().mixture().nMonomer();
      int meshSize = system().domain().mesh().size();
 
      // Check array capacities
      UTIL_CHECK(etaA_.capacity() == nMonomer-1);
      UTIL_CHECK(etaB_.capacity() == nMonomer-1);
      for (int i=0; i < nMonomer - 1; ++i) {
         UTIL_CHECK(etaA_[i].capacity() == meshSize);
         UTIL_CHECK(etaB_[i].capacity() == meshSize);
      }
      UTIL_CHECK(dwc_.capacity() == meshSize);
 
      // Initialize pointers
      etaOldPtr_ = &etaA_;
      etaNewPtr_ = &etaB_;
 
      generateEtaNew();
      exchangeOldNew();
   }
 
   /*
   * One step of Leimkuhler-Matthews BD algorithm.
   */
   template <int D>
   bool LMBdStep<D>::step()
   {
      // Array sizes and indices
      const int nMonomer = system().mixture().nMonomer();
      const int meshSize = system().domain().mesh().size();
      int i, j, k;
 
      // Save current state
      simulator().saveState();
 
      // Copy current fields to w_
      for (i = 0; i < nMonomer; ++i) {
         w_[i] = system().w().rgrid(i);
      }
 
      // Generate new random displacement values
      generateEtaNew();
 
      // Take LM step:
      const double a = -1.0*mobility_;
      double evec;
      // Loop over composition eigenvectors of projected chi matrix
      for (j = 0; j < nMonomer - 1; ++j) {
         RField<D> const & etaN = etaNew(j);
         RField<D> const & etaO = etaOld(j);
         RField<D> const & dc = simulator().dc(j);
         for (k = 0; k < meshSize; ++k) {
            dwc_[k] = a*dc[k] + etaN[k] + etaO[k];
         }
         // Loop over monomer types
         for (i = 0; i < nMonomer; ++i) {
            RField<D> & w = w_[i];
            evec = simulator().chiEvecs(j,i);
            for (k = 0; k < meshSize; ++k) {
               w[k] += evec*dwc_[k];
            }
         }
      }
 
      // Set modified fields
      system().w().setRGrid(w_);
 
      // Enforce incompressibility (also solves MDE repeatedly)
      bool isConverged = false;
      int compress = simulator().compressor().compress();
      if (compress != 0){
         simulator().restoreState();
      } else {
         isConverged = true;
         UTIL_CHECK(system().c().hasData());
 
         // Compute components and derivatives at wp_
         simulator().clearState();
         simulator().clearData();
         simulator().computeWc();
         simulator().computeCc();
         simulator().computeDc();
 
         // Exchange old and new random fields
         exchangeOldNew();
 
      }
 
      return isConverged;
   }
 
}
}
#endif