HeteQuadrature/examples/examples_quad_multipoly.cpp

// Examples to demonstrate Algoim's methods for computing high-order accurate quadrature schemes
// on multi-component domains implicitly-defined by (one or more) multivariate Bernstein
// polynomials. Additional examples are provided on the GitHub documentation page,
// https://algoim.github.io/

#include <cstddef>
#include <iostream>
#include <iomanip>
#include <fstream>
#include <vector>
#include "bernstein.hpp"
#include "quadrature_multipoly.hpp"

#include "uvector.hpp"
#include "vector"
#include "xarray.hpp"

#include "myDebug.hpp"
#include "primitiveDebug.hpp"
#include "PMTest.hpp"

using namespace algoim;

const static std::vector<std::vector<real>> binomial_table = {
    {1, 0, 0,  0,  0,  0, 0},
    {1, 1, 0,  0,  0,  0, 0},
    {1, 2, 1,  0,  0,  0, 0},
    {1, 3, 3,  1,  0,  0, 0},
    {1, 4, 6,  4,  1,  0, 0},
    {1, 5, 10, 10, 5,  1, 0},
    {1, 6, 15, 20, 15, 6, 1}
};

// function模板不允许直接<部分>特化，所以用类模板
template <int N>
struct DebugXArray {
    template <typename Phi>
    void operator()(const xarray<real, N>& iData, Phi&& phi)
    {
    }
};

template <>
struct DebugXArray<2> {
    template <typename Phi>
    void operator()(const xarray<real, 2>& iData, Phi&& phi)
    {
        std::vector<std::vector<real>> data(iData.ext(0), std::vector<real>(iData.ext(1)));
        for (int i = 0; i < iData.ext(0); ++i) {
            for (int j = 0; j < iData.ext(1); ++j) { data[i][j] = iData(i, j); }
        }
        real              inputX1 = 0.2, inputX2 = 0.3;
        std::vector<real> b1(iData.ext(0)), b2(iData.ext(1));
        int               n1 = iData.ext(0) - 1, n2 = iData.ext(1) - 1;
        real              res = 0;
        for (int i = 0; i < iData.ext(0); ++i) {
            b1[i] = binomial_table[n1][i] * std::pow(inputX1, i) * std::pow(1 - inputX1, n1 - i);
        }
        for (int i = 0; i < iData.ext(1); ++i) {
            b2[i] = binomial_table[n2][i] * std::pow(inputX2, i) * std::pow(1 - inputX2, n2 - i);
        }
        for (int i = 0; i < iData.ext(0); ++i) {
            real tmp = 0;
            for (int j = 0; j < iData.ext(1); j++) { tmp += data[i][j] * b2[j]; }
            res += tmp * b1[i];
        }

        // original phi function evaluation
        const uvector<real, 2> x(inputX1, inputX2);
        real                   phiEval = phi(x);
    }
};

// Driver method which takes a functor phi defining a single polynomial in the reference
// rectangle [xmin, xmax]^N, of Bernstein degree P, along with an integrand function,
// and performances a q-refinement convergence study, comparing the computed integral
// with the given exact answers, for 1 <= q <= qMax.
template <int N, typename Phi, typename F>
void qConv(const Phi&      phi,
           real            xmin,
           real            xmax,
           uvector<int, N> P,
           const F&        integrand,
           int             qMax,
           real            volume_exact,
           real            surf_exact)
{
    // Construct Bernstein polynomial by mapping [0,1] onto bounding box [xmin,xmax]
    xarray<real, N> phipoly(nullptr, P);
    algoim_spark_alloc(real, phipoly);
    bernstein::bernsteinInterpolate<N>([&](const uvector<real, N>& x) { return phi(xmin + x * (xmax - xmin)); }, phipoly);
    DebugXArray<N>()(phipoly, [&](const uvector<real, N>& x) { return phi(xmin + x * (xmax - xmin)); });

    // Build quadrature hierarchy
    ImplicitPolyQuadrature<N> ipquad(phipoly);

    // Functional to evaluate volume and surface integrals of given integrand
    real volume, surf;
    auto compute = [&](int q) {
        volume = 0.0;
        surf   = 0.0;
        // compute volume integral over {phi < 0} using AutoMixed strategy
        ipquad.integrate(AutoMixed, q, [&](const uvector<real, N>& x, real w) {
            if (bernstein::evalBernsteinPoly(phipoly, x) < 0) volume += w * integrand(xmin + x * (xmax - xmin));
        });
        // compute surface integral over {phi == 0} using AutoMixed strategy
        ipquad.integrate_surf(AutoMixed, q, [&](const uvector<real, N>& x, real w, const uvector<real, N>& wn) {
            surf += w * integrand(xmin + x * (xmax - xmin));
        });
        // scale appropriately
        volume *= pow(xmax - xmin, N);
        surf   *= pow(xmax - xmin, N - 1);
    };

    // Compute results for all q and output in a convergence table
    for (int q = 1; q <= qMax; ++q) {
        compute(q);
        std::cout << q << ' ' << volume << ' ' << surf << ' ' << std::abs(volume - volume_exact) / volume_exact << ' '
                  << std::abs(surf - surf_exact) / surf_exact << std::endl;
    }
}

template <typename Phi, typename F>
void debug3D(const Phi&      phi,
             real            xmin,
             real            xmax,
             uvector<int, 3> P,
             const F&        integrand,
             int             q,
             real            volume_exact,
             real            surf_exact)
{
    // Construct Bernstein polynomial by mapping [0,1] onto bounding box [xmin,xmax]
    xarray<real, 3> phipoly(nullptr, P);
    algoim_spark_alloc(real, phipoly);
    bernstein::bernsteinInterpolate<3>([&](const uvector<real, 3>& x) { return phi(xmin + x * (xmax - xmin)); }, phipoly);
    DebugXArray<3>()(phipoly, [&](const uvector<real, 3>& x) { return phi(xmin + x * (xmax - xmin)); });

    uvector<real, 3> testX(0., 0., 0.5);
    real             testEvalBernstein = bernstein::evalBernsteinPoly(phipoly, testX);
    std::cout << "eval bernstein using interpolation:" << testEvalBernstein << std::endl;

    // Build quadrature hierarchy
    ImplicitPolyQuadrature<3> ipquad(phipoly);

    // Functional to evaluate volume and surface integrals of given integrand
    real volume, surf;
    auto compute = [&](int q) {
        volume = 0.0;
        surf   = 0.0;
        // compute volume integral over {phi < 0} using AutoMixed strategy
        ipquad.integrate(AutoMixed, q, [&](const uvector<real, 3>& x, real w) {
            if (bernstein::evalBernsteinPoly(phipoly, x) < 0) volume += w * integrand(xmin + x * (xmax - xmin));
        });
        // compute surface integral over {phi == 0} using AutoMixed strategy
        ipquad.integrate_surf(AutoMixed, q, [&](const uvector<real, 3>& x, real w, const uvector<real, 3>& wn) {
            surf += w * integrand(xmin + x * (xmax - xmin));
        });
        // scale appropriately
        volume *= pow(xmax - xmin, 3);
        surf   *= pow(xmax - xmin, 3 - 1);
    };

    // Compute results for all q and output in a convergence table
    compute(q);
    std::cout << "volume: " << volume << std::endl;
}

// Given a set of quadrature points and weights, output them to an VTP XML file for visualisation
// purposes, e.g., using ParaView
template <int N>
void outputQuadratureRuleAsVtpXML(const std::vector<uvector<real, N + 1>>& q, std::string fn)
{
    static_assert(N == 2 || N == 3, "outputQuadratureRuleAsVtpXML only supports 2D and 3D quadrature schemes");
    std::ofstream stream(fn);
    stream << "<?xml version=\"1.0\"?>\n";
    stream << "<VTKFile type=\"PolyData\" version=\"0.1\" byte_order=\"LittleEndian\">\n";
    stream << "<PolyData>\n";
    stream << "<Piece NumberOfPoints=\"" << q.size() << "\" NumberOfVerts=\"" << q.size()
           << "\" NumberOfLines=\"0\" NumberOfStrips=\"0\" NumberOfPolys=\"0\">\n";
    stream << "<Points>\n";
    stream << "  <DataArray type=\"Float32\" Name=\"Points\" NumberOfComponents=\"3\" format=\"ascii\">";
    for (const auto& pt : q) stream << pt(0) << ' ' << pt(1) << ' ' << (N == 3 ? pt(2) : 0.0) << ' ';
    stream << "</DataArray>\n";
    stream << "</Points>\n";
    stream << "<Verts>\n";
    stream << "  <DataArray type=\"Int32\" Name=\"connectivity\" format=\"ascii\">";
    for (size_t i = 0; i < q.size(); ++i) stream << i << ' ';
    stream << "</DataArray>\n";
    stream << "  <DataArray type=\"Int32\" Name=\"offsets\" format=\"ascii\">";
    for (size_t i = 1; i <= q.size(); ++i) stream << i << ' ';
    stream << "</DataArray>\n";
    stream << "</Verts>\n";
    stream << "<PointData Scalars=\"w\">\n";
    stream << "  <DataArray type=\"Float32\" Name=\"w\" NumberOfComponents=\"1\" format=\"ascii\">";
    for (const auto& pt : q) stream << pt(N) << ' ';
    stream << "</DataArray>\n";
    stream << "</PointData>\n";
    stream << "</Piece>\n";
    stream << "</PolyData>\n";
    stream << "</VTKFile>\n";
};

// Driver method which takes a functor phi defining a single polynomial in the reference
// rectangle [xmin, xmax]^N, of Bernstein degree P, builds a quadrature scheme with the
// given q, and outputs it for visualisation in a set of VTP XML files
template <int N, typename F>
void outputQuadScheme(const F& fphi, real xmin, real xmax, const uvector<int, N>& P, int q, std::string qfile)
{
    // Construct phi by mapping [0,1] onto bounding box [xmin,xmax]
    xarray<real, N> phi(nullptr, P);
    algoim_spark_alloc(real, phi);
    bernstein::bernsteinInterpolate<N>([&](const uvector<real, N>& x) { return fphi(xmin + x * (xmax - xmin)); }, phi);

    // Build quadrature hierarchy
    ImplicitPolyQuadrature<N> ipquad(phi);

    // Compute quadrature scheme and record the nodes & weights; phase0 corresponds to
    // {phi < 0}, phase1 corresponds to {phi > 0}, and surf corresponds to {phi == 0}.
    std::vector<uvector<real, N + 1>> phase0, phase1, surf;
    ipquad.integrate(AutoMixed, q, [&](const uvector<real, N>& x, real w) {
        if (bernstein::evalBernsteinPoly(phi, x) < 0)
            phase0.push_back(add_component(x, N, w));
        else
            phase1.push_back(add_component(x, N, w));
    });
    ipquad.integrate_surf(AutoMixed, q, [&](const uvector<real, N>& x, real w, const uvector<real, N>& wn) {
        surf.push_back(add_component(x, N, w));
    });

    // output to file
    outputQuadratureRuleAsVtpXML<N>(phase0, qfile + "-phase0.vtp");
    outputQuadratureRuleAsVtpXML<N>(phase1, qfile + "-phase1.vtp");
    outputQuadratureRuleAsVtpXML<N>(surf, qfile + "-surf.vtp");
}

// Driver method which takes two phi functors defining two polynomials in the reference
// rectangle [xmin, xmax]^N, each of of Bernstein degree P, builds a quadrature scheme with the
// given q, and outputs it for visualisation in a set of VTP XML files
template <int N, typename F1, typename F2>
void outputQuadScheme(const F1&              fphi1,
                      const F2&              fphi2,
                      real                   xmin,
                      real                   xmax,
                      const uvector<int, N>& P,
                      int                    q,
                      std::string            qfile)
{
    // Construct phi by mapping [0,1] onto bounding box [xmin,xmax]
    xarray<real, N> phi1(nullptr, P), phi2(nullptr, P);
    algoim_spark_alloc(real, phi1, phi2);
    bernstein::bernsteinInterpolate<N>([&](const uvector<real, N>& x) { return fphi1(xmin + x * (xmax - xmin)); }, phi1);
    bernstein::bernsteinInterpolate<N>([&](const uvector<real, N>& x) { return fphi2(xmin + x * (xmax - xmin)); }, phi2);

    // Build quadrature hierarchy
    ImplicitPolyQuadrature<N> ipquad(phi1, phi2);

    // Compute quadrature scheme and record the nodes & weights; one could examine the signs
    // of phi1 and phi2 in order to separate the nodes into different components, but for
    // simplicity they are agglomerated
    std::vector<uvector<real, N + 1>> vol, surf;
    ipquad.integrate(AutoMixed, q, [&](const uvector<real, N>& x, real w) { vol.push_back(add_component(x, N, w)); });
    ipquad.integrate_surf(AutoMixed, q, [&](const uvector<real, N>& x, real w, const uvector<real, N>& wn) {
        surf.push_back(add_component(x, N, w));
    });

    // output to a file
    outputQuadratureRuleAsVtpXML<N>(vol, qfile + "-vol.vtp");
    outputQuadratureRuleAsVtpXML<N>(surf, qfile + "-surf.vtp");
}

void module_test()
{
    if (false) {
        const uvector<int, 1> P(5);
        xarray<real, 1>       beta(nullptr, P);
        algoim_spark_alloc(real, beta);
        for (int i = 0; i < 5; i++) beta[i] = i + 1;
        const uvector<real, 1> x(0.5);
        auto                   res = bernstein::evalBernsteinPoly(beta, x);
        std::cout << "res: " << res << std::endl;
    }
    if (true) {
        const uvector<int, 2> P(4, 4);
        xarray<real, 2>       beta(nullptr, P);
        algoim_spark_alloc(real, beta);
        for (int i = 0; i < 4; i++)
            for (int j = 0; j < 4; j++) { beta(i, j) = i + j; }
        const uvector<real, 2> x(0.5, 0.3);
        auto                   res = bernstein::evalBernsteinPoly(beta, x);
        std::cout << "res: " << res << std::endl;
    }
}

#if ALGOIM_EXAMPLES_DRIVER == 0 || ALGOIM_EXAMPLES_DRIVER == 4
int main(int argc, char* argv[])
{
    std::cout << "Algoim Examples - High-order quadrature algorithms for multi-component domains implicitly-defined\n";
    std::cout << "by (one or more) multivariate Bernstein polynomials\n\n";
    std::cout << std::scientific << std::setprecision(10);

    // q-convergence study for a 2D ellipse
    if (false) {
        auto ellipse      = [](const uvector<real, 2>& x) { return x(0) * x(0) + x(1) * x(1) * 4 - 1; };
        auto integrand    = [](const uvector<real, 2>& x) { return 1.0; };
        real volume_exact = algoim::util::pi / 2;
        real surf_exact   = 4.844224110273838099214251598195914705976959198943300412541558176231060;
        std::cout << "\n\nEllipse q-convergence test\n";
        std::cout << "q      area(q)         perim(q)        area error       perim error\n"; // perimeter: 周长
        qConv<2>(ellipse, -1.1, 1.1, 3, integrand, 50, volume_exact, surf_exact);
    }

    // q-convergence study for a 3D ellipsoid
    if (false) {
        auto ellipsoid    = [](const uvector<real, 3>& x) { return x(0) * x(0) + x(1) * x(1) * 4 + x(2) * x(2) * 9 - 1; };
        auto integrand    = [](const uvector<real, 3>& x) { return 1.0; };
        real volume_exact = (algoim::util::pi * 2) / 9;
        real surf_exact   = 4.400809564664970341600200389229705943483674323377145800356686868037845;
        std::cout << "\n\nEllipsoid q-convergence test\n";
        std::cout << "q      volume(q)         surf(q)        vol error       surf error\n";
        qConv<3>(ellipsoid, -1.1, 1.1, 3, integrand, 50, volume_exact, surf_exact);
    }

    // Visusalisation of a 2D case involving a single polynomial; this example corresponds to
    // Figure 3, row 3, left column, https://doi.org/10.1016/j.jcp.2021.110720
    if (false) {
        auto phi = [](const uvector<real, 2>& xx) {
            real x = xx(0) * 2 - 1;
            real y = xx(1) * 2 - 1;
            return -0.06225100787918392 + 0.1586472897571363 * y + 0.5487135634635731 * y * y
                   + x * (0.3478849533965025 - 0.3321074999999999 * y - 0.5595163485848738 * y * y)
                   + x * x * (0.7031095851739786 + 0.29459557349175747 * y + 0.030425624999999998 * y * y);
        };
        outputQuadScheme<2>(phi, 0.0, 1.0, 3, 3, "exampleA");
        std::cout << "\n\nQuadrature visualisation of a 2D case involving a single polynomial, corresponding\n";
        std::cout << "to Figure 3, row 3, left column, https://doi.org/10.1016/j.jcp.2021.110720, written\n";
        std::cout << "to exampleA-xxxx.vtp files (XML VTP file format).";
    }

    // Visusalisation of a 3D case involving a single polynomial; this example corresponds to
    // Figure 3, row 3, right column, https://doi.org/10.1016/j.jcp.2021.110720
    if (false) {
        auto phi = [](const uvector<real, 3>& xx) {
            real x = xx(0) * 2 - 1;
            real y = xx(1) * 2 - 1;
            real z = xx(2) * 2 - 1;
            return -0.3003521613375472 - 0.22416584292513722 * z + 0.07904600284034838 * z * z
                   + y * (-0.022501556528537706 - 0.16299445153615613 * z - 0.10968042065096766 * z * z)
                   + y * y * (0.09321375574517882 - 0.07409794846221623 * z + 0.09940785133211516 * z * z)
                   + x
                         * (0.094131400740032 - 0.11906280402685224 * z - 0.010060302873268541 * z * z
                            + y * y * (0.01448948481714108 - 0.0262370580373332 * z - 0.08632912757566019 * z * z)
                            + y * (0.08171132326327647 - 0.09286444275596013 * z - 0.07651000354823911 * z * z))
                   + x * x
                         * (-0.0914370528387867 + 0.09778971384044874 * z - 0.1086777644685091 * z * z
                            + y * y * (-0.04283439400630859 + 0.0750156999192893 * z + 0.051754527934553866 * z * z)
                            + y * (-0.052642188754328405 - 0.03538476045586772 * z + 0.11117016852276898 * z * z));
        };
        outputQuadScheme<3>(phi, 0.0, 1.0, 3, 3, "exampleB");
        std::cout << "\n\nQuadrature visualisation of a 3D case involving a single polynomial, corresponding\n";
        std::cout << "to Figure 3, row 3, right column, https://doi.org/10.1016/j.jcp.2021.110720, written\n";
        std::cout << "to exampleB-xxxx.vtp files (XML VTP file format).";
    }

    // Visusalisation of a 2D implicitly-defined domain involving the intersection of two polynomials; this example
    // corresponds to the top-left example of Figure 15, https://doi.org/10.1016/j.jcp.2021.110720
    if (false) {
        auto phi0 = [](const uvector<real, 2>& xx) {
            real x = xx(0) * 2 - 1;
            real y = xx(1) * 2 - 1;
            return 0.014836540349115947 + 0.7022484024095262 * y + 0.09974561176434385 * y * y
                   + x * (0.6863910464417281 + 0.03805619999999999 * y - 0.09440658332756446 * y * y)
                   + x * x * (0.19266932968830816 - 0.2325190091204104 * y + 0.2957473125000001 * y * y);
        };
        auto phi1 = [](const uvector<real, 2>& xx) {
            real x = xx(0) * 2 - 1;
            real y = xx(1) * 2 - 1;
            return -0.18792528379702625 + 0.6713882473904913 * y + 0.3778666084723582 * y * y
                   + x * x * (-0.14480813208127946 + 0.0897755603159206 * y - 0.141199875 * y * y)
                   + x * (-0.6169311810674598 - 0.19449299999999994 * y - 0.005459163675646665 * y * y);
        };
        outputQuadScheme<2>(phi0, phi1, 0.0, 1.0, 3, 3, "exampleC");
        std::cout << "\n\nQuadrature visualisation of a 2D implicitly-defined domain involving the\n";
        std::cout << "intersection of two polynomials, corresponding to the top-left example of Figure 15,\n";
        std::cout << "https://doi.org/10.1016/j.jcp.2021.110720, written to exampleC-xxxx.vtp files\n";
        std::cout << "(XML VTP file format).\n";
    }

    // a 3D sphere
    if (false) {
        auto ellipsoid    = [](const uvector<real, 3>& x) { return x(0) * x(0) + x(1) * x(1) + x(2) * x(2) - 1; };
        auto integrand    = [](const uvector<real, 3>& x) { return 1.0; };
        real volume_exact = (algoim::util::pi * 2) / 9;
        real surf_exact   = 4.400809564664970341600200389229705943483674323377145800356686868037845;
        std::cout << "\n\nEllipsoid q-convergence test\n";
        std::cout << "q      volume(q)         surf(q)        vol error       surf error\n";
        debug3D(ellipsoid, -1., 1., 3, integrand, 10, volume_exact, surf_exact);
    }

    // module_test();
    // testMain();
    // testPrimitive();
    testPM();
    return 0;
}

#endif