blockoperator.cpp

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// Copyright (c) 2010-2026, Lawrence Livermore National Security, LLC. Produced
// at the Lawrence Livermore National Laboratory. All Rights reserved. See files
// LICENSE and NOTICE for details. LLNL-CODE-806117.
//
// This file is part of the MFEM library. For more information and source code
// availability visit https://mfem.org.
//
// MFEM is free software; you can redistribute it and/or modify it under the
// terms of the BSD-3 license. We welcome feedback and contributions, see file
// CONTRIBUTING.md for details.
 
#include "../general/array.hpp"
#include "operator.hpp"
#include "blockvector.hpp"
#include "blockoperator.hpp"
 
 
namespace mfem
{
 
BlockOperator::BlockOperator(const Array<int> &offsets)
   : Operator(offsets.Last()),
     owns_blocks(0),
     nRowBlocks(offsets.Size() - 1),
     nColBlocks(offsets.Size() - 1),
     row_offsets(offsets),
     col_offsets(offsets),
     op(nRowBlocks, nRowBlocks),
     coef(nRowBlocks, nColBlocks)
{
   op = nullptr;
}
 
BlockOperator::BlockOperator(const Array<int> &row_offsets_,
                             const Array<int> &col_offsets_)
   : Operator(row_offsets_.Last(), col_offsets_.Last()),
     owns_blocks(0),
     nRowBlocks(row_offsets_.Size()-1),
     nColBlocks(col_offsets_.Size()-1),
     row_offsets(row_offsets_),
     col_offsets(col_offsets_),
     op(nRowBlocks, nColBlocks),
     coef(nRowBlocks, nColBlocks)
{
   op = nullptr;
}
 
void BlockOperator::SetDiagonalBlock(int iblock, Operator *opt, real_t c)
{
   SetBlock(iblock, iblock, opt, c);
}
 
void BlockOperator::SetBlock(int iRow, int iCol, Operator *opt, real_t c)
{
   if (owns_blocks && op(iRow, iCol))
   {
      delete op(iRow, iCol);
   }
   op(iRow, iCol) = opt;
   coef(iRow, iCol) = c;
 
   MFEM_VERIFY(row_offsets[iRow+1] - row_offsets[iRow] == opt->NumRows() &&
               col_offsets[iCol+1] - col_offsets[iCol] == opt->NumCols(),
               "incompatible Operator dimensions");
}
 
// Operator application
void BlockOperator::Mult(const Vector &x, Vector &y) const
{
   MFEM_ASSERT(x.Size() == width, "incorrect input Vector size");
   MFEM_ASSERT(y.Size() == height, "incorrect output Vector size");
 
   x.Read();
   y.Write();
   y = 0.0;
 
   xblock.Update(const_cast<Vector&>(x), col_offsets);
   yblock.Update(y, row_offsets);
 
   for (int iRow=0; iRow < nRowBlocks; ++iRow)
   {
      tmp.SetSize(row_offsets[iRow+1] - row_offsets[iRow]);
      tmp.UseDevice(true);
      for (int jCol=0; jCol < nColBlocks; ++jCol)
      {
         if (op(iRow,jCol) && coef(iRow,jCol) != 0.)
         {
            op(iRow,jCol)->Mult(xblock.GetBlock(jCol), tmp);
            yblock.GetBlock(iRow).Add(coef(iRow,jCol), tmp);
         }
      }
   }
 
   for (int iRow=0; iRow < nRowBlocks; ++iRow)
   {
      yblock.GetBlock(iRow).SyncAliasMemory(y);
   }
}
 
// Action of the transpose operator
void BlockOperator::MultTranspose(const Vector &x, Vector &y) const
{
   MFEM_ASSERT(x.Size() == height, "incorrect input Vector size");
   MFEM_ASSERT(y.Size() == width, "incorrect output Vector size");
 
   x.Read();
   y.Write();
   y = 0.0;
 
   xblock.Update(const_cast<Vector&>(x), row_offsets);
   yblock.Update(y, col_offsets);
 
   for (int iRow=0; iRow < nColBlocks; ++iRow)
   {
      tmp.SetSize(col_offsets[iRow+1] - col_offsets[iRow]);
      tmp.UseDevice(true);
      for (int jCol=0; jCol < nRowBlocks; ++jCol)
      {
         if (op(jCol,iRow) && coef(jCol,iRow) != 0.)
         {
            op(jCol,iRow)->MultTranspose(xblock.GetBlock(jCol), tmp);
            yblock.GetBlock(iRow).Add(coef(jCol,iRow), tmp);
         }
      }
   }
 
   for (int iRow=0; iRow < nColBlocks; ++iRow)
   {
      yblock.GetBlock(iRow).SyncAliasMemory(y);
   }
}
 
#ifdef MFEM_USE_MPI
 
HypreParMatrix * BlockOperator::GetMonolithicHypreParMatrix() const
{
   Array2D<const HypreParMatrix*> blocks(nRowBlocks, nColBlocks);
   for (int i = 0; i < nRowBlocks; ++i)
   {
      for (int j = 0; j < nColBlocks; ++j)
      {
         if (IsZeroBlock(i, j))
         {
            blocks(i, j) = nullptr;
         }
         else
         {
            auto mat = dynamic_cast<const HypreParMatrix*>(&GetBlock(i, j));
            MFEM_VERIFY(mat,"BlockOperator block (" << i << "," << j
                        << ") is not a HypreParMatrix.");
            blocks(i, j) = mat;
         }
      }
   }
   Array2D<real_t> coef_mut = coef;   // make a non-const copy
   return HypreParMatrixFromBlocks(blocks, &coef_mut);
}
#endif
 
BlockOperator::~BlockOperator()
{
   if (owns_blocks)
   {
      for (int iRow=0; iRow < nRowBlocks; ++iRow)
      {
         for (int jCol=0; jCol < nColBlocks; ++jCol)
         {
            delete op(iRow, jCol);
         }
      }
   }
}
 
BlockDiagonalPreconditioner::BlockDiagonalPreconditioner(
   const Array<int> & offsets_):
   Solver(offsets_.Last()),
   owns_blocks(0),
   nBlocks(offsets_.Size() - 1),
   offsets(0),
   ops(nBlocks)
{
   ops = nullptr;
   offsets.MakeRef(offsets_);
}
 
void BlockDiagonalPreconditioner::SetDiagonalBlock(int iblock, Operator *op)
{
   MFEM_VERIFY(offsets[iblock+1] - offsets[iblock] == op->Height() &&
               offsets[iblock+1] - offsets[iblock] == op->Width(),
               "incompatible Operator dimensions");
 
   if (owns_blocks && ops[iblock])
   {
      delete ops[iblock];
   }
   ops[iblock] = op;
}
 
// Operator application
void BlockDiagonalPreconditioner::Mult(const Vector &x, Vector &y) const
{
   MFEM_ASSERT(x.Size() == width, "incorrect input Vector size");
   MFEM_ASSERT(y.Size() == height, "incorrect output Vector size");
 
   x.Read();
   y.Write();
   y = 0.0;
 
   xblock.Update(const_cast<Vector&>(x), offsets);
   yblock.Update(y, offsets);
 
   for (int i=0; i<nBlocks; ++i)
   {
      if (ops[i])
      {
         ops[i]->Mult(xblock.GetBlock(i), yblock.GetBlock(i));
      }
      else
      {
         yblock.GetBlock(i) = xblock.GetBlock(i);
      }
   }
 
   for (int i=0; i<nBlocks; ++i)
   {
      yblock.GetBlock(i).SyncAliasMemory(y);
   }
}
 
// Action of the transpose operator
void BlockDiagonalPreconditioner::MultTranspose(const Vector & x,
                                                Vector & y) const
{
   MFEM_ASSERT(x.Size() == height, "incorrect input Vector size");
   MFEM_ASSERT(y.Size() == width, "incorrect output Vector size");
 
   x.Read();
   y.Write();
   y = 0.0;
 
   xblock.Update(const_cast<Vector&>(x),offsets);
   yblock.Update(y,offsets);
 
   for (int i=0; i<nBlocks; ++i)
   {
      if (ops[i])
      {
         (ops[i])->MultTranspose(xblock.GetBlock(i), yblock.GetBlock(i));
      }
      else
      {
         yblock.GetBlock(i) = xblock.GetBlock(i);
      }
   }
 
   for (int i=0; i<nBlocks; ++i)
   {
      yblock.GetBlock(i).SyncAliasMemory(y);
   }
}
 
BlockDiagonalPreconditioner::~BlockDiagonalPreconditioner()
{
   if (owns_blocks)
   {
      for (int i=0; i<nBlocks; ++i)
      {
         delete ops[i];
      }
   }
}
 
BlockLowerTriangularPreconditioner::BlockLowerTriangularPreconditioner(
   const Array<int> & offsets_)
   : Solver(offsets_.Last()),
     owns_blocks(0),
     nBlocks(offsets_.Size() - 1),
     offsets(0),
     ops(nBlocks, nBlocks)
{
   ops = nullptr;
   offsets.MakeRef(offsets_);
}
 
void BlockLowerTriangularPreconditioner::SetDiagonalBlock(int iblock,
                                                          Operator *op)
{
   MFEM_VERIFY(offsets[iblock+1] - offsets[iblock] == op->Height() &&
               offsets[iblock+1] - offsets[iblock] == op->Width(),
               "incompatible Operator dimensions");
 
   SetBlock(iblock, iblock, op);
}
 
void BlockLowerTriangularPreconditioner::SetBlock(int iRow, int iCol,
                                                  Operator *op)
{
   MFEM_VERIFY(iRow >= iCol,"cannot set block in upper triangle");
   MFEM_VERIFY(offsets[iRow+1] - offsets[iRow] == op->NumRows() &&
               offsets[iCol+1] - offsets[iCol] == op->NumCols(),
               "incompatible Operator dimensions");
 
   ops(iRow, iCol) = op;
}
 
// Operator application
void BlockLowerTriangularPreconditioner::Mult(const Vector &x,
                                              Vector &y) const
{
   MFEM_ASSERT(x.Size() == width, "incorrect input Vector size");
   MFEM_ASSERT(y.Size() == height, "incorrect output Vector size");
 
   x.Read();
   y.Write();
   y = 0.0;
 
   xblock.Update(const_cast<Vector&>(x),offsets);
   yblock.Update(y,offsets);
 
   for (int iRow=0; iRow < nBlocks; ++iRow)
   {
      tmp.SetSize(offsets[iRow+1] - offsets[iRow]);
      tmp.UseDevice(true);
      tmp2.SetSize(offsets[iRow+1] - offsets[iRow]);
      tmp2.UseDevice(true);
      tmp2 = 0.0;
      tmp2 += xblock.GetBlock(iRow);
      for (int jCol=0; jCol < iRow; ++jCol)
      {
         if (ops(iRow,jCol))
         {
            ops(iRow,jCol)->Mult(yblock.GetBlock(jCol), tmp);
            tmp2 -= tmp;
         }
      }
      if (ops(iRow,iRow))
      {
         ops(iRow,iRow)->Mult(tmp2, yblock.GetBlock(iRow));
      }
      else
      {
         yblock.GetBlock(iRow) = tmp2;
      }
   }
 
   for (int iRow=0; iRow < nBlocks; ++iRow)
   {
      yblock.GetBlock(iRow).SyncAliasMemory(y);
   }
}
 
// Action of the transpose operator
void BlockLowerTriangularPreconditioner::MultTranspose(const Vector &x,
                                                       Vector &y) const
{
   MFEM_ASSERT(x.Size() == height, "incorrect input Vector size");
   MFEM_ASSERT(y.Size() == width, "incorrect output Vector size");
 
   x.Read();
   y.Write();
   y = 0.0;
 
   xblock.Update(const_cast<Vector&>(x), offsets);
   yblock.Update(y, offsets);
 
   for (int iRow=nBlocks-1; iRow >=0; --iRow)
   {
      tmp.SetSize(offsets[iRow+1] - offsets[iRow]);
      tmp.UseDevice(true);
      tmp2.SetSize(offsets[iRow+1] - offsets[iRow]);
      tmp2.UseDevice(true);
      tmp2 = 0.0;
      tmp2 += xblock.GetBlock(iRow);
      for (int jCol=iRow+1; jCol < nBlocks; ++jCol)
      {
         if (ops(jCol,iRow))
         {
            ops(jCol,iRow)->MultTranspose(yblock.GetBlock(jCol), tmp);
            tmp2 -= tmp;
         }
      }
      if (ops(iRow,iRow))
      {
         ops(iRow,iRow)->MultTranspose(tmp2, yblock.GetBlock(iRow));
      }
      else
      {
         yblock.GetBlock(iRow) = tmp2;
      }
   }
 
   for (int iRow=nBlocks-1; iRow >=0; --iRow)
   {
      yblock.GetBlock(iRow).SyncAliasMemory(y);
   }
}
 
BlockLowerTriangularPreconditioner::~BlockLowerTriangularPreconditioner()
{
   if (owns_blocks)
   {
      for (int iRow=0; iRow < nBlocks; ++iRow)
      {
         for (int jCol=0; jCol < nBlocks; ++jCol)
         {
            delete ops(jCol,iRow);
         }
      }
   }
}
 
} // namespace mfem