acoustics.cpp

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// Copyright (c) 2010-2025, 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.
//
//                   MFEM Ultraweak DPG example for acoustics (Helmholtz)
//
// Compile with: make acoustics
//
// Sample runs
//
//  acoustics -ref 4 -o 1 -rnum 1.0
//  acoustics -m ../../data/inline-tri.mesh -ref 4 -o 2 -sc -rnum 3.0
//  acoustics -m ../../data/amr-quad.mesh -ref 3 -o 3 -sc -rnum 4.5 -prob 1
//  acoustics -m ../../data/inline-quad.mesh -ref 2 -o 4 -sc -rnum 11.5 -prob 1
//  acoustics -m ../../data/inline-hex.mesh -ref 1 -o 2 -sc -rnum 1.0
 
// Description:
// This example code demonstrates the use of MFEM to define and solve
// the "ultraweak" (UW) DPG formulation for the Helmholtz problem
 
//     - Δ p - ω² p = f̃ ,   in Ω
//                p = p₀, on ∂Ω
 
// It solves two kinds of problems
// a) f̃ = 0 and p₀ is a plane wave
// b) A manufactured solution problem where p_exact is a gaussian beam
// This example computes and prints out convergence rates for the L² error.
 
// The DPG UW deals with the First Order System
//  ∇ p + i ω u = 0, in Ω
//  ∇⋅u + i ω p = f, in Ω              (1)
//           p = p_0, in ∂Ω
// where f:=f̃/(i ω)
 
// Ultraweak-DPG is obtained by integration by parts of both equations and the
// introduction of trace unknowns on the mesh skeleton
//
// p ∈ L²(Ω), u ∈ (L²(Ω))ᵈⁱᵐ
// p̂ ∈ H^1/2(Ω), û ∈ H^-1/2(Ω)
// -(p,  ∇⋅v) + i ω (u , v) + < p̂, v⋅n> = 0,      ∀ v ∈ H(div,Ω)
// -(u , ∇ q) + i ω (p , q) + < û, q >  = (f,q)   ∀ q ∈ H¹(Ω)
//                                   p̂  = p₀      on ∂Ω
 
// Note:
// p̂ := p, û := u on the mesh skeleton
 
// For more information see https://doi.org/10.1016/j.camwa.2017.06.044
 
// -------------------------------------------------------------
// |   |     p     |     u     |    p̂      |    û    |  RHS    |
// -------------------------------------------------------------
// | v | -(p, ∇⋅v) | i ω (u,v) | < p̂, v⋅n> |         |         |
// |   |           |           |           |         |         |
// | q | i ω (p,q) |-(u , ∇ q) |           | < û,q > |  (f,q)  |
 
// where (q,v) ∈  H¹(Ω) × H(div,Ω)
 
// Here we use the "Adjoint Graph" norm on the test space i.e.,
// ||(q,v)||²ᵥ = ||A^*(q,v)||² + ||(q,v)||² where A is the
// acoustics operator defined by (1)
 
#include "mfem.hpp"
#include "util/complexweakform.hpp"
#include "../common/mfem-common.hpp"
#include <fstream>
#include <iostream>
 
using namespace std;
using namespace mfem;
using namespace mfem::common;
 
complex<real_t> acoustics_solution(const Vector & X);
void acoustics_solution_grad(const Vector & X,vector<complex<real_t>> &dp);
complex<real_t> acoustics_solution_laplacian(const Vector & X);
 
real_t p_exact_r(const Vector &x);
real_t p_exact_i(const Vector &x);
void u_exact_r(const Vector &x, Vector & u);
void u_exact_i(const Vector &x, Vector & u);
real_t rhs_func_r(const Vector &x);
real_t rhs_func_i(const Vector &x);
void gradp_exact_r(const Vector &x, Vector &gradu);
void gradp_exact_i(const Vector &x, Vector &gradu);
real_t divu_exact_r(const Vector &x);
real_t divu_exact_i(const Vector &x);
real_t d2_exact_r(const Vector &x);
real_t d2_exact_i(const Vector &x);
real_t hatp_exact_r(const Vector & X);
real_t hatp_exact_i(const Vector & X);
void hatu_exact_r(const Vector & X, Vector & hatu);
void hatu_exact_i(const Vector & X, Vector & hatu);
 
int dim;
real_t omega;
 
enum prob_type
{
   plane_wave,
   gaussian_beam
};
 
prob_type prob;
 
int main(int argc, char *argv[])
{
   const char *mesh_file = "../../data/inline-quad.mesh";
   int order = 1;
   int delta_order = 1;
   bool visualization = true;
   real_t rnum=1.0;
   int ref = 0;
   bool static_cond = false;
   int visport = 19916;
   int iprob = 0;
 
   OptionsParser args(argc, argv);
   args.AddOption(&mesh_file, "-m", "--mesh",
                  "Mesh file to use.");
   args.AddOption(&order, "-o", "--order",
                  "Finite element order (polynomial degree)");
   args.AddOption(&visualization, "-vis", "--visualization", "-no-vis",
                  "--no-visualization",
                  "Enable or disable GLVis visualization.");
   args.AddOption(&rnum, "-rnum", "--number_of_wavelengths",
                  "Number of wavelengths");
   args.AddOption(&iprob, "-prob", "--problem", "Problem case"
                  " 0: plane wave, 1: Gaussian beam");
   args.AddOption(&delta_order, "-do", "--delta_order",
                  "Order enrichment for DPG test space.");
   args.AddOption(&ref, "-ref", "--refinements",
                  "Number of serial refinements.");
   args.AddOption(&static_cond, "-sc", "--static-condensation", "-no-sc",
                  "--no-static-condensation", "Enable static condensation.");
   args.AddOption(&visport, "-p", "--send-port", "Socket for GLVis.");
   args.Parse();
   if (!args.Good())
   {
      args.PrintUsage(cout);
      return 1;
   }
   args.PrintOptions(cout);
 
   if (iprob > 1) { iprob = 0; }
   prob = (prob_type)iprob;
 
   omega = 2.*M_PI*rnum;
 
   Mesh mesh(mesh_file, 1, 1);
   dim = mesh.Dimension();
   MFEM_VERIFY(dim > 1, "Dimension = 1 is not supported in this example");
 
   // Define spaces
   enum TrialSpace
   {
      p_space     = 0,
      u_space     = 1,
      hatp_space  = 2,
      hatu_space  = 3
   };
   enum TestSpace
   {
      q_space = 0,
      v_space = 1
   };
 
   // L2 space for p
   FiniteElementCollection *p_fec = new L2_FECollection(order-1,dim);
   FiniteElementSpace *p_fes = new FiniteElementSpace(&mesh,p_fec);
 
   // Vector L2 space for u
   FiniteElementCollection *u_fec = new L2_FECollection(order-1,dim);
   FiniteElementSpace *u_fes = new FiniteElementSpace(&mesh,u_fec, dim);
 
   // H^1/2 space for p̂
   FiniteElementCollection * hatp_fec = new H1_Trace_FECollection(order,dim);
   FiniteElementSpace *hatp_fes = new FiniteElementSpace(&mesh,hatp_fec);
 
   // H^-1/2 space for û
   FiniteElementCollection * hatu_fec = new RT_Trace_FECollection(order-1,dim);
   FiniteElementSpace *hatu_fes = new FiniteElementSpace(&mesh,hatu_fec);
 
   // testspace fe collections
   int test_order = order+delta_order;
   FiniteElementCollection * q_fec = new H1_FECollection(test_order, dim);
   FiniteElementCollection * v_fec = new RT_FECollection(test_order-1, dim);
 
   // Coefficients
   ConstantCoefficient one(1.0);
   ConstantCoefficient zero(0.0);
   Vector vec0(dim); vec0 = 0.;
   VectorConstantCoefficient vzero(vec0);
   ConstantCoefficient negone(-1.0);
   ConstantCoefficient omeg(omega);
   ConstantCoefficient omeg2(omega*omega);
   ConstantCoefficient negomeg(-omega);
 
   Array<FiniteElementSpace * > trial_fes;
   Array<FiniteElementCollection * > test_fec;
 
   trial_fes.Append(p_fes);
   trial_fes.Append(u_fes);
   trial_fes.Append(hatp_fes);
   trial_fes.Append(hatu_fes);
 
   test_fec.Append(q_fec);
   test_fec.Append(v_fec);
 
   ComplexDPGWeakForm * a = new ComplexDPGWeakForm(trial_fes,test_fec);
 
   // i ω (p,q)
   a->AddTrialIntegrator(nullptr,new MixedScalarMassIntegrator(omeg),
                         TrialSpace::p_space,TestSpace::q_space);
   // -(u , ∇ q)
   a->AddTrialIntegrator(new TransposeIntegrator(new GradientIntegrator(negone)),
                         nullptr,TrialSpace::u_space,TestSpace::q_space);
   // -(p, ∇⋅v)
   a->AddTrialIntegrator(new MixedScalarWeakGradientIntegrator(one),nullptr,
                         TrialSpace::p_space,TestSpace::v_space);
   //  i ω (u,v)
   a->AddTrialIntegrator(nullptr,
                         new TransposeIntegrator(new VectorFEMassIntegrator(omeg)),
                         TrialSpace::u_space,TestSpace::v_space);
   // < p̂, v⋅n>
   a->AddTrialIntegrator(new NormalTraceIntegrator,nullptr,
                         TrialSpace::hatp_space,TestSpace::v_space);
   // < û,q >
   a->AddTrialIntegrator(new TraceIntegrator,nullptr,
                         TrialSpace::hatu_space,TestSpace::q_space);
 
   // test space integrators (Adjoint graph norm)
   // (∇q,∇δq)
   a->AddTestIntegrator(new DiffusionIntegrator(one),nullptr,
                        TestSpace::q_space, TestSpace::q_space);
   // (q,δq)
   a->AddTestIntegrator(new MassIntegrator(one),nullptr,
                        TestSpace::q_space, TestSpace::q_space);
   // (∇⋅v,∇⋅δv)
   a->AddTestIntegrator(new DivDivIntegrator(one),nullptr,
                        TestSpace::v_space, TestSpace::v_space);
   // (v,δv)
   a->AddTestIntegrator(new VectorFEMassIntegrator(one),nullptr,
                        TestSpace::v_space, TestSpace::v_space);
   // -i ω (∇q,δv)
   a->AddTestIntegrator(nullptr,new MixedVectorGradientIntegrator(negomeg),
                        TestSpace::q_space, TestSpace::v_space);
   // i ω (v,∇ δq)
   a->AddTestIntegrator(nullptr,new MixedVectorWeakDivergenceIntegrator(negomeg),
                        TestSpace::v_space, TestSpace::q_space);
   // ω^2 (v,δv)
   a->AddTestIntegrator(new VectorFEMassIntegrator(omeg2),nullptr,
                        TestSpace::v_space, TestSpace::v_space);
   // - i ω (∇⋅v,δq)
   a->AddTestIntegrator(nullptr,new VectorFEDivergenceIntegrator(negomeg),
                        TestSpace::v_space, TestSpace::q_space);
   // i ω (q,∇⋅v)
   a->AddTestIntegrator(nullptr,new MixedScalarWeakGradientIntegrator(negomeg),
                        TestSpace::q_space, TestSpace::v_space);
   // ω^2 (q,δq)
   a->AddTestIntegrator(new MassIntegrator(omeg2),nullptr,
                        TestSpace::q_space, TestSpace::q_space);
 
   // RHS
   FunctionCoefficient f_rhs_r(rhs_func_r);
   FunctionCoefficient f_rhs_i(rhs_func_i);
   if (prob == prob_type::gaussian_beam)
   {
      a->AddDomainLFIntegrator(new DomainLFIntegrator(f_rhs_r),
                               new DomainLFIntegrator(f_rhs_i), TestSpace::q_space);
   }
 
   FunctionCoefficient hatpex_r(hatp_exact_r);
   FunctionCoefficient hatpex_i(hatp_exact_i);
   VectorFunctionCoefficient hatuex_r(dim,hatu_exact_r);
   VectorFunctionCoefficient hatuex_i(dim,hatu_exact_i);
 
   socketstream p_out_r;
   socketstream p_out_i;
 
   real_t err0 = 0.;
   int dof0 = 0; // init to suppress gcc warning
 
   std::cout << "\n  Ref |"
             << "    Dofs    |"
             << "    ω    |"
             << "  L2 Error  |"
             << "  Rate  |"
             << " PCG it |" << endl;
   std::cout << std::string(60,'-')
             << endl;
 
   for (int it = 0; it<=ref; it++)
   {
      if (static_cond) { a->EnableStaticCondensation(); }
      a->Assemble();
 
      Array<int> ess_tdof_list;
      Array<int> ess_bdr;
      if (mesh.bdr_attributes.Size())
      {
         ess_bdr.SetSize(mesh.bdr_attributes.Max());
         ess_bdr = 1;
         hatp_fes->GetEssentialTrueDofs(ess_bdr, ess_tdof_list);
      }
 
      // shift the ess_tdofs
      for (int j = 0; j < ess_tdof_list.Size(); j++)
      {
         ess_tdof_list[j] += p_fes->GetTrueVSize() + u_fes->GetTrueVSize();
      }
 
      Array<int> offsets(5);
      offsets[0] = 0;
      offsets[1] = p_fes->GetVSize();
      offsets[2] = u_fes->GetVSize();
      offsets[3] = hatp_fes->GetVSize();
      offsets[4] = hatu_fes->GetVSize();
      offsets.PartialSum();
 
      Vector x(2*offsets.Last());
      x = 0.;
 
      GridFunction hatp_gf_r(hatp_fes, x, offsets[2]);
      GridFunction hatp_gf_i(hatp_fes, x, offsets.Last()+ offsets[2]);
      hatp_gf_r.ProjectBdrCoefficient(hatpex_r, ess_bdr);
      hatp_gf_i.ProjectBdrCoefficient(hatpex_i, ess_bdr);
 
      OperatorPtr Ah;
      Vector X,B;
      a->FormLinearSystem(ess_tdof_list,x,Ah, X,B);
 
      // Setup operator and preconditioner
      ComplexOperator * Ahc = Ah.As<ComplexOperator>();
 
      BlockMatrix * A_r = dynamic_cast<BlockMatrix *>(&Ahc->real());
      BlockMatrix * A_i = dynamic_cast<BlockMatrix *>(&Ahc->imag());
 
      int num_blocks = A_r->NumRowBlocks();
      Array<int> tdof_offsets(2*num_blocks+1);
      tdof_offsets[0] = 0;
      int k = (static_cond) ? 2 : 0;
      for (int i=0; i<num_blocks; i++)
      {
         tdof_offsets[i+1] = trial_fes[i+k]->GetTrueVSize();
         tdof_offsets[num_blocks+i+1] = trial_fes[i+k]->GetTrueVSize();
      }
      tdof_offsets.PartialSum();
 
      BlockOperator A(tdof_offsets);
      for (int i = 0; i<num_blocks; i++)
      {
         for (int j = 0; j<num_blocks; j++)
         {
            A.SetBlock(i,j,&A_r->GetBlock(i,j));
            A.SetBlock(i,j+num_blocks,&A_i->GetBlock(i,j), -1.0);
            A.SetBlock(i+num_blocks,j+num_blocks,&A_r->GetBlock(i,j));
            A.SetBlock(i+num_blocks,j,&A_i->GetBlock(i,j));
         }
      }
 
      BlockDiagonalPreconditioner M(tdof_offsets);
      M.owns_blocks = 1;
      for (int i = 0; i<num_blocks; i++)
      {
         M.SetDiagonalBlock(i, new GSSmoother((SparseMatrix&)A_r->GetBlock(i,i)));
         M.SetDiagonalBlock(num_blocks+i, new GSSmoother((SparseMatrix&)A_r->GetBlock(i,
                                                                                      i)));
      }
 
      CGSolver cg;
      cg.SetRelTol(1e-10);
      cg.SetMaxIter(2000);
      cg.SetPrintLevel(0);
      cg.SetPreconditioner(M);
      cg.SetOperator(A);
      cg.Mult(B, X);
 
      a->RecoverFEMSolution(X,x);
 
      GridFunction p_r(p_fes, x, 0);
      GridFunction p_i(p_fes, x, offsets.Last());
 
      GridFunction u_r(u_fes, x, offsets[1]);
      GridFunction u_i(u_fes, x, offsets.Last() + offsets[1]);
 
      FunctionCoefficient p_ex_r(p_exact_r);
      FunctionCoefficient p_ex_i(p_exact_i);
 
      VectorFunctionCoefficient u_ex_r(dim,u_exact_r);
      VectorFunctionCoefficient u_ex_i(dim,u_exact_i);
 
      int dofs = 0;
      for (int i = 0; i<trial_fes.Size(); i++)
      {
         dofs += trial_fes[i]->GetTrueVSize();
      }
 
      real_t p_err_r = p_r.ComputeL2Error(p_ex_r);
      real_t p_err_i = p_i.ComputeL2Error(p_ex_i);
      real_t u_err_r = u_r.ComputeL2Error(u_ex_r);
      real_t u_err_i = u_i.ComputeL2Error(u_ex_i);
 
      real_t L2Error = sqrt(p_err_r*p_err_r + p_err_i*p_err_i
                            +u_err_r*u_err_r + u_err_i*u_err_i);
 
      real_t rate_err = (it) ? dim*log(err0/L2Error)/log((real_t)dof0/dofs) : 0.0;
 
      err0 = L2Error;
      dof0 = dofs;
 
      std::ios oldState(nullptr);
      oldState.copyfmt(std::cout);
      std::cout << std::right << std::setw(5) << it << " | "
                << std::setw(10) <<  dof0 << " | "
                << std::setprecision(1) << std::fixed
                << std::setw(4) <<  2*rnum << " π  | "
                << std::setprecision(3)
                << std::setw(10) << std::scientific << err0 << " | "
                << std::setprecision(2)
                << std::setw(6) << std::fixed << rate_err << " | "
                << std::setw(6) << std::fixed << cg.GetNumIterations() << " | "
                << std::endl;
      std::cout.copyfmt(oldState);
 
      if (visualization)
      {
         const char * keys = (it == 0 && dim == 2) ? "jRcml\n" : nullptr;
         char vishost[] = "localhost";
         VisualizeField(p_out_r,vishost, visport, p_r,
                        "Numerical presure (real part)", 0, 0, 500, 500, keys);
         VisualizeField(p_out_i,vishost, visport, p_i,
                        "Numerical presure (imaginary part)", 501, 0, 500, 500, keys);
      }
 
      if (it == ref)
      {
         break;
      }
 
      mesh.UniformRefinement();
      for (int i =0; i<trial_fes.Size(); i++)
      {
         trial_fes[i]->Update(false);
      }
      a->Update();
   }
 
   delete a;
   delete q_fec;
   delete v_fec;
   delete hatp_fes;
   delete hatp_fec;
   delete hatu_fes;
   delete hatu_fec;
   delete u_fec;
   delete p_fec;
   delete u_fes;
   delete p_fes;
 
   return 0;
}
 
real_t p_exact_r(const Vector &x)
{
   return acoustics_solution(x).real();
}
 
real_t p_exact_i(const Vector &x)
{
   return acoustics_solution(x).imag();
}
 
real_t hatp_exact_r(const Vector & X)
{
   return p_exact_r(X);
}
 
real_t hatp_exact_i(const Vector & X)
{
   return p_exact_i(X);
}
 
void gradp_exact_r(const Vector &x, Vector &grad_r)
{
   grad_r.SetSize(x.Size());
   vector<complex<real_t>> grad;
   acoustics_solution_grad(x,grad);
   for (unsigned i = 0; i < grad.size(); i++)
   {
      grad_r[i] = grad[i].real();
   }
}
 
void gradp_exact_i(const Vector &x, Vector &grad_i)
{
   grad_i.SetSize(x.Size());
   vector<complex<real_t>> grad;
   acoustics_solution_grad(x,grad);
   for (unsigned i = 0; i < grad.size(); i++)
   {
      grad_i[i] = grad[i].imag();
   }
}
 
real_t d2_exact_r(const Vector &x)
{
 
   return acoustics_solution_laplacian(x).real();
}
 
real_t d2_exact_i(const Vector &x)
{
   return acoustics_solution_laplacian(x).imag();
}
 
//  u = - ∇ p / (i ω )
//    = i (∇ p_r + i * ∇ p_i)  / ω
//    = - ∇ p_i / ω + i ∇ p_r / ω
void u_exact_r(const Vector &x, Vector & u)
{
   gradp_exact_i(x,u);
   u *= -1./omega;
}
 
void u_exact_i(const Vector &x, Vector & u)
{
   gradp_exact_r(x,u);
   u *= 1./omega;
}
 
void hatu_exact_r(const Vector & X, Vector & hatu)
{
   u_exact_r(X,hatu);
}
void hatu_exact_i(const Vector & X, Vector & hatu)
{
   u_exact_i(X,hatu);
}
 
//  ∇⋅u = i Δ p / ω
//      = i (Δ p_r + i * Δ p_i)  / ω
//      = - Δ p_i / ω + i Δ p_r / ω
real_t divu_exact_r(const Vector &x)
{
   return -d2_exact_i(x)/omega;
}
 
real_t divu_exact_i(const Vector &x)
{
   return d2_exact_r(x)/omega;
}
 
// f = ∇⋅u + i ω p
// f_r = ∇⋅u_r - ω p_i
real_t rhs_func_r(const Vector &x)
{
   real_t p = p_exact_i(x);
   real_t divu = divu_exact_r(x);
   return divu - omega * p;
}
 
// f_i = ∇⋅u_i + ω p_r
real_t rhs_func_i(const Vector &x)
{
   real_t p = p_exact_r(x);
   real_t divu = divu_exact_i(x);
   return divu + omega * p;
}
 
complex<real_t> acoustics_solution(const Vector & X)
{
   complex<real_t> zi = complex<real_t>(0., 1.);
   switch (prob)
   {
      case plane_wave:
      {
         real_t beta = omega/std::sqrt((real_t)X.Size());
         complex<real_t> alpha = beta * zi * X.Sum();
         return exp(alpha);
      }
      break;
      default:
      {
         real_t rk = omega;
         real_t degrees = 45;
         real_t alpha = (180+degrees) * M_PI/180.;
         real_t sina = sin(alpha);
         real_t cosa = cos(alpha);
         // shift the origin
         real_t xprim=X(0) + 0.1;
         real_t yprim=X(1) + 0.1;
 
         real_t  x = xprim*sina - yprim*cosa;
         real_t  y = xprim*cosa + yprim*sina;
         //wavelength
         real_t rl = 2.*M_PI/rk;
         // beam waist radius
         real_t w0 = 0.05;
         // function w
         real_t fact = rl/M_PI/(w0*w0);
         real_t aux = 1. + (fact*y)*(fact*y);
         real_t w = w0*sqrt(aux);
         real_t phi0 = atan(fact*y);
         real_t r = y + 1./y/(fact*fact);
 
         // pressure
         complex<real_t> ze = - x*x/(w*w) - zi*rk*y - zi * real_t(M_PI) * x * x/rl/r +
                              zi*phi0/2_r;
 
         real_t pf = pow(2.0/M_PI/(w*w),0.25);
         return pf*exp(ze);
      }
      break;
   }
}
 
void acoustics_solution_grad(const Vector & X, vector<complex<real_t>> & dp)
{
   dp.resize(X.Size());
   complex<real_t> zi = complex<real_t>(0., 1.);
   switch (prob)
   {
      case plane_wave:
      {
         real_t beta = omega/std::sqrt((real_t)X.Size());
         complex<real_t> alpha = beta * zi * X.Sum();
         complex<real_t> p = exp(alpha);
         for (int i = 0; i<X.Size(); i++)
         {
            dp[i] = zi * beta * p;
         }
      }
      break;
      default:
      {
         real_t rk = omega;
         real_t degrees = 45;
         real_t alpha = (180+degrees) * M_PI/180.;
         real_t sina = sin(alpha);
         real_t cosa = cos(alpha);
         // shift the origin
         real_t xprim=X(0) + 0.1;
         real_t yprim=X(1) + 0.1;
 
         real_t  x = xprim*sina - yprim*cosa;
         real_t  y = xprim*cosa + yprim*sina;
         real_t  dxdxprim = sina, dxdyprim = -cosa;
         real_t  dydxprim = cosa, dydyprim =  sina;
         //wavelength
         real_t rl = 2.*M_PI/rk;
 
         // beam waist radius
         real_t w0 = 0.05;
 
         // function w
         real_t fact = rl/M_PI/(w0*w0);
         real_t aux = 1. + (fact*y)*(fact*y);
 
         real_t w = w0*sqrt(aux);
         real_t dwdy = w0*fact*fact*y/sqrt(aux);
 
         real_t phi0 = atan(fact*y);
         real_t dphi0dy = cos(phi0)*cos(phi0)*fact;
 
         real_t r = y + 1./y/(fact*fact);
         real_t drdy = 1. - 1./(y*y)/(fact*fact);
 
         constexpr real_t r2 = 2.0;
         const real_t rPI = M_PI;
 
         // pressure
         complex<real_t> ze = - x*x/(w*w) - zi*rk*y - zi * rPI * x * x/rl/r +
                              zi*phi0/r2;
 
         complex<real_t> zdedx = -r2*x/(w*w) - r2*zi*rPI*x/rl/r;
         complex<real_t> zdedy = r2*x*x/(w*w*w)*dwdy - zi*rk + zi*rPI*x*x/rl/
                                 (r*r)*drdy + zi*dphi0dy/r2;
 
         real_t pf = pow(2.0/M_PI/(w*w),0.25);
         real_t dpfdy = -pow(2./M_PI/(w*w),-0.75)/M_PI/(w*w*w)*dwdy;
 
         complex<real_t> zp = pf*exp(ze);
         complex<real_t> zdpdx = zp*zdedx;
         complex<real_t> zdpdy = dpfdy*exp(ze)+zp*zdedy;
 
         dp[0] = (zdpdx*dxdxprim + zdpdy*dydxprim);
         dp[1] = (zdpdx*dxdyprim + zdpdy*dydyprim);
         if (dim == 3) { dp[2] = 0.0; }
      }
      break;
   }
}
 
complex<real_t> acoustics_solution_laplacian(const Vector & X)
{
   complex<real_t> zi = complex<real_t>(0., 1.);
   switch (prob)
   {
      case plane_wave:
      {
         real_t beta = omega/std::sqrt((real_t)X.Size());
         complex<real_t> alpha = beta * zi * X.Sum();
         complex<real_t> p = exp(alpha);
         return dim * beta * beta * p;
      }
      break;
      default:
      {
         real_t rk = omega;
         real_t degrees = 45;
         real_t alpha = (180+degrees) * M_PI/180.;
         real_t sina = sin(alpha);
         real_t cosa = cos(alpha);
         // shift the origin
         real_t xprim=X(0) + 0.1;
         real_t yprim=X(1) + 0.1;
 
         real_t  x = xprim*sina - yprim*cosa;
         real_t  y = xprim*cosa + yprim*sina;
         real_t  dxdxprim = sina, dxdyprim = -cosa;
         real_t  dydxprim = cosa, dydyprim =  sina;
         //wavelength
         real_t rl = 2.*M_PI/rk;
 
         // beam waist radius
         real_t w0 = 0.05;
 
         // function w
         real_t fact = rl/M_PI/(w0*w0);
         real_t aux = 1. + (fact*y)*(fact*y);
 
         real_t w = w0*sqrt(aux);
         real_t dwdy = w0*fact*fact*y/sqrt(aux);
         real_t d2wdydy = w0*fact*fact*(1. - (fact*y)*(fact*y)/aux)/sqrt(aux);
 
         real_t phi0 = atan(fact*y);
         real_t dphi0dy = cos(phi0)*cos(phi0)*fact;
         real_t d2phi0dydy = -2.*cos(phi0)*sin(phi0)*fact*dphi0dy;
 
         real_t r = y + 1./y/(fact*fact);
         real_t drdy = 1. - 1./(y*y)/(fact*fact);
         real_t d2rdydy = 2./(y*y*y)/(fact*fact);
 
         constexpr real_t r2 = 2.0;
         const real_t rPI = M_PI;
 
         // pressure
         complex<real_t> ze = - x*x/(w*w) - zi*rk*y - zi * rPI * x * x/rl/r +
                              zi*phi0/r2;
 
         complex<real_t> zdedx = -r2*x/(w*w) - r2*zi*rPI*x/rl/r;
         complex<real_t> zdedy = r2*x*x/(w*w*w)*dwdy - zi*rk + zi*rPI*x*x/rl/
                                 (r*r)*drdy + zi*dphi0dy/r2;
         complex<real_t> zd2edxdx = -r2/(w*w) - r2*zi*rPI/rl/r;
         complex<real_t> zd2edxdy = 4_r*x/(w*w*w)*dwdy + r2*zi*rPI*x/rl/(r*r)*drdy;
         complex<real_t> zd2edydx = zd2edxdy;
         complex<real_t> zd2edydy = -6_r*x*x/(w*w*w*w)*dwdy*dwdy + r2*x*x/
                                    complex<real_t>(w*w*w)*d2wdydy - r2*zi*rPI*x*x/rl/(r*r*r)*drdy*drdy
                                    + zi*rPI*x*x/rl/(r*r)*d2rdydy + zi/r2*d2phi0dydy;
 
         real_t pf = pow(2.0/M_PI/(w*w),0.25);
         real_t dpfdy = -pow(2./M_PI/(w*w),-0.75)/M_PI/(w*w*w)*dwdy;
         real_t d2pfdydy = -1./M_PI*pow(2./M_PI,-0.75)*(-1.5*pow(w,-2.5)
                                                        *dwdy*dwdy + pow(w,-1.5)*d2wdydy);
 
         complex<real_t> zp = pf*exp(ze);
         complex<real_t> zdpdx = zp*zdedx;
         complex<real_t> zdpdy = dpfdy*exp(ze)+zp*zdedy;
         complex<real_t> zd2pdxdx = zdpdx*zdedx + zp*zd2edxdx;
         complex<real_t> zd2pdxdy = zdpdy*zdedx + zp*zd2edxdy;
         complex<real_t> zd2pdydx = dpfdy*exp(ze)*zdedx + zdpdx*zdedy + zp*zd2edydx;
         complex<real_t> zd2pdydy = d2pfdydy*exp(ze) + dpfdy*exp(
                                       ze)*zdedy + zdpdy*zdedy + zp*zd2edydy;
 
 
         return (zd2pdxdx*dxdxprim + zd2pdydx*dydxprim)*dxdxprim
                + (zd2pdxdy*dxdxprim + zd2pdydy*dydxprim)*dydxprim
                + (zd2pdxdx*dxdyprim + zd2pdydx*dydyprim)*dxdyprim
                + (zd2pdxdy*dxdyprim + zd2pdydy*dydyprim)*dydyprim;
      }
      break;
   }
}