main_eigen.cpp

#include "Grid/grid_dist_id.hpp"
#include "Matrix/SparseMatrix.hpp"
#include "Vector/Vector.hpp"
#include "FiniteDifference/FDScheme.hpp"
#include "FiniteDifference/util/common.hpp"
#include "FiniteDifference/eq.hpp"
#include "Solvers/umfpack_solver.hpp"
#include "Solvers/petsc_solver.hpp"

struct lid_nn
{
    // dimensionaly of the equation (2D problem 3D problem ...)
    static const unsigned int dims = 2;

    // number of fields in the system v_x, v_y, P so a total of 3
    static const unsigned int nvar = 3;

    // boundary conditions PERIODIC OR NON_PERIODIC
    static const bool boundary[];

    // type of space float, double, ...
    typedef float stype;

    // type of base grid, it is the distributed grid that will store the result
    // Note the first property is a 2D vector (velocity), the second is a scalar (Pressure)
    typedef grid_dist_id<2,float,aggregate<float[2],float>,CartDecomposition<2,float>> b_grid;

    // type of SparseMatrix, for the linear system, this parameter is bounded by the solver
    // that you are using, in case of umfpack using <double,int> it is the only possible choice
    // By default SparseMatrix is EIGEN based
    typedef SparseMatrix<double,int> SparseMatrix_type;

    // type of Vector for the linear system, this parameter is bounded by the solver
    // that you are using, in case of umfpack using <double> it is the only possible choice
    typedef Vector<double> Vector_type;

    // Define that the underline grid where we discretize the system of equation is staggered
    static const int grid_type = STAGGERED_GRID;
};

const bool lid_nn::boundary[] = {NON_PERIODIC,NON_PERIODIC};




// Constant Field
struct eta
{
    typedef void const_field;

    static float val()  {return 1.0;}
};

// Convenient constants
constexpr unsigned int v[] = {0,1};
constexpr unsigned int P = 2;
constexpr unsigned int ic = 2;
constexpr int x = 0;
constexpr int y = 1;

// Create field that we have v_x, v_y, P
typedef Field<v[x],lid_nn> v_x;                 // Definition 1 v_x
typedef Field<v[y],lid_nn> v_y;                 // Definition 2 v_y
typedef Field<P,lid_nn> Prs;                    // Definition 3 Prs

// Eq1 V_x

typedef mul<eta,Lap<v_x,lid_nn>,lid_nn> eta_lap_vx;       // Step 1
typedef D<x,Prs,lid_nn> p_x;                              // Step 2
typedef minus<p_x,lid_nn> m_p_x;                          // Step 3
typedef sum<eta_lap_vx,m_p_x,lid_nn> vx_eq;               // Step 4

// Eq2 V_y

typedef mul<eta,Lap<v_y,lid_nn>,lid_nn> eta_lap_vy;
typedef D<y,Prs,lid_nn> p_y;
typedef minus<p_y,lid_nn> m_p_y;
typedef sum<eta_lap_vy,m_p_y,lid_nn> vy_eq;

// Eq3 Incompressibility

typedef D<x,v_x,lid_nn,FORWARD> dx_vx;                   // Step 5
typedef D<y,v_y,lid_nn,FORWARD> dy_vy;                   // Step 6
typedef sum<dx_vx,dy_vy,lid_nn> ic_eq;                   // Step 7



// Equation for boundary conditions

// Directional Avg
typedef Avg<x,v_y,lid_nn> avg_vy;
typedef Avg<y,v_x,lid_nn> avg_vx;

typedef Avg<x,v_y,lid_nn,FORWARD> avg_vy_f;
typedef Avg<y,v_x,lid_nn,FORWARD> avg_vx_f;

// Usefull constants (as MACRO)
#define EQ_1 0
#define EQ_2 1
#define EQ_3 2


#include "Vector/vector_dist.hpp"
#include "data_type/aggregate.hpp"

int main(int argc, char* argv[])
{

    // Initialize
    openfpm_init(&argc,&argv);

    // velocity in the grid is the property 0, pressure is the property 1
    constexpr int velocity = 0;
    constexpr int pressure = 1;

    // Domain, a rectangle
    Box<2,float> domain({0.0,0.0},{3.0,1.0});

    // Ghost (Not important in this case but required)
    Ghost<2,float> g(0.01);

    // Grid points on x=256 and y=64
    long int sz[] = {96,32};
    size_t szu[2];
    szu[0] = (size_t)sz[0];
    szu[1] = (size_t)sz[1];

    // We need one more point on the left and down part of the domain
    // This is given by the boundary conditions that we impose.
    //
    Padding<2> pd({1,1},{0,0});



    grid_dist_id<2,float,aggregate<float[2],float>> g_dist(szu,domain,g);



    // It is the maximum extension of the stencil (order 2 laplacian stencil has extension 1)
    Ghost<2,long int> stencil_max(1);

    // Finite difference scheme
    FDScheme<lid_nn> fd(pd, stencil_max, domain, g_dist);



    fd.impose(ic_eq(),0.0, EQ_3, {0,0},{sz[0]-2,sz[1]-2},true);
    fd.impose(Prs(),  0.0, EQ_3, {0,0},{0,0});

    // Here we impose the Eq1 and Eq2
    fd.impose(vx_eq(),0.0, EQ_1, {1,0},{sz[0]-2,sz[1]-2});
    fd.impose(vy_eq(),0.0, EQ_2, {0,1},{sz[0]-2,sz[1]-2});

    // v_x and v_y
    // Imposing B1
    fd.impose(v_x(),0.0, EQ_1, {0,0},{0,sz[1]-2});
    fd.impose(avg_vy_f(),0.0, EQ_2 , {-1,0},{-1,sz[1]-1});
    // Imposing B2
    fd.impose(v_x(),0.0, EQ_1, {sz[0]-1,0},{sz[0]-1,sz[1]-2});
    fd.impose(avg_vy(),1.0, EQ_2,    {sz[0]-1,0},{sz[0]-1,sz[1]-1});

    // Imposing B3
    fd.impose(avg_vx_f(),0.0, EQ_1, {0,-1},{sz[0]-1,-1});
    fd.impose(v_y(), 0.0, EQ_2, {0,0},{sz[0]-2,0});
    // Imposing B4
    fd.impose(avg_vx(),0.0, EQ_1,   {0,sz[1]-1},{sz[0]-1,sz[1]-1});
    fd.impose(v_y(), 0.0, EQ_2, {0,sz[1]-1},{sz[0]-2,sz[1]-1});

    // When we pad the grid, there are points of the grid that are not
    // touched by the previous condition. Mathematically this lead
    // to have too many variables for the conditions that we are imposing.
    // Here we are imposing variables that we do not touch to zero
    //

    // Padding pressure
    fd.impose(Prs(), 0.0, EQ_3, {-1,-1},{sz[0]-1,-1});
    fd.impose(Prs(), 0.0, EQ_3, {-1,sz[1]-1},{sz[0]-1,sz[1]-1});
    fd.impose(Prs(), 0.0, EQ_3, {-1,0},{-1,sz[1]-2});
    fd.impose(Prs(), 0.0, EQ_3, {sz[0]-1,0},{sz[0]-1,sz[1]-2});

    // Impose v_x Padding Impose v_y padding
    fd.impose(v_x(), 0.0, EQ_1, {-1,-1},{-1,sz[1]-1});
    fd.impose(v_y(), 0.0, EQ_2, {-1,-1},{sz[0]-1,-1});



    // Create an UMFPACK solver
    umfpack_solver<double> solver;

    // Give to the solver A and b, return x, the solution
    auto x = solver.solve(fd.getA(),fd.getB());



    fd.template copy<velocity,pressure>(x,{0,0},{sz[0]-1,sz[1]-1},g_dist);

    g_dist.write("lid_driven_cavity_p_umfpack");




    openfpm_finalize();



}