DGMSolver.cpp

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#include "moab/DiscreteGeometry/DGMSolver.hpp"
#include "moab/ErrorHandler.hpp"
#include <iostream>
#include <cassert>
#include <vector>
#include <limits>
#include <cmath>
#include <algorithm>

namespace moab
{

/* This class implements the lowest level solvers required by polynomial fitting for high-order
 * reconstruction. An underlying assumption of the matrices passed are that they are given in a
 * column-major form. So, the first mrows values of V is the first column, and so on. This
 * assumption is made because most of the operations are column-based in the current scenario.
 * */

unsigned int DGMSolver::nchoosek( unsigned int n, unsigned int k )
{
    if( k > n )
    {
        return 0;
    }
    unsigned long long ans = 1;
    if( k > ( n >> 1 ) )
    {
        k = n - k;
    }
    for( unsigned int i = 1; i <= k; ++i )
    {
        ans *= n--;
        ans /= i;
        if( ans > std::numeric_limits< unsigned int >::max() )
        {
            return 0;
        }
    }
    return ans;
}

unsigned int DGMSolver::compute_numcols_vander_multivar( unsigned int kvars, unsigned int degree )
{
    unsigned int mcols = 0;
    for( unsigned int i = 0; i <= degree; ++i )
    {
        unsigned int temp = nchoosek( kvars - 1 + i, kvars - 1 );
        if( !temp )
        {
            std::cout << "overflow to compute nchoosek n= " << kvars - 1 + i << " k= " << kvars - 1 << std::endl;
            return 0;
        }
        mcols += temp;
    }
    return mcols;
}

void DGMSolver::gen_multivar_monomial_basis( const int kvars,
                                             const double* vars,
                                             const int degree,
                                             std::vector< double >& basis )
{
    unsigned int len = compute_numcols_vander_multivar( kvars, degree );
    basis.reserve( len - basis.capacity() + basis.size() );
    size_t iend = basis.size();
#ifndef NDEBUG
    size_t istr = basis.size();
#endif
    basis.push_back( 1 );
    ++iend;
    if( !degree )
    {
        return;
    }
    std::vector< size_t > varspos( kvars );
    // degree 1
    for( int ivar = 0; ivar < kvars; ++ivar )
    {
        basis.push_back( vars[ivar] );
        varspos[ivar] = iend++;
    }
    // degree 2 to degree
    for( int ideg = 2; ideg <= degree; ++ideg )
    {
        size_t preend = iend;
        for( int ivar = 0; ivar < kvars; ++ivar )
        {
            size_t varpreend = iend;
            for( size_t ilast = varspos[ivar]; ilast < preend; ++ilast )
            {
                basis.push_back( vars[ivar] * basis[ilast] );
                ++iend;
            }
            varspos[ivar] = varpreend;
        }
    }
    assert( len == iend - istr );
}

void DGMSolver::gen_vander_multivar( const int mrows,
                                     const int kvars,
                                     const double* us,
                                     const int degree,
                                     std::vector< double >& V )
{
    unsigned int ncols = compute_numcols_vander_multivar( kvars, degree );
    V.reserve( mrows * ncols - V.capacity() + V.size() );
    size_t istr = V.size(), icol = 0;
    // add ones, V is stored in an single array, elements placed in columnwise order
    for( int irow = 0; irow < mrows; ++irow )
    {
        V.push_back( 1 );
    }
    ++icol;
    if( !degree )
    {
        return;
    }
    std::vector< size_t > varspos( kvars );
    // degree 1
    for( int ivar = 0; ivar < kvars; ++ivar )
    {
        for( int irow = 0; irow < mrows; ++irow )
        {
            V.push_back( us[irow * kvars + ivar] );  // us stored in row-wise
        }
        varspos[ivar] = icol++;
    }
    // from 2 to degree
    for( int ideg = 2; ideg <= degree; ++ideg )
    {
        size_t preendcol = icol;
        for( int ivar = 0; ivar < kvars; ++ivar )
        {
            size_t varpreend = icol;
            for( size_t ilast = varspos[ivar]; ilast < preendcol; ++ilast )
            {
                for( int irow = 0; irow < mrows; ++irow )
                {
                    V.push_back( us[irow * kvars + ivar] * V[istr + irow + ilast * mrows] );
                }
                ++icol;
            }
            varspos[ivar] = varpreend;
        }
    }
    assert( icol == ncols );
}

void DGMSolver::rescale_matrix( int mrows, int ncols, double* V, double* ts )
{
    // This function rescales the input matrix using the norm of each column.
    double* v = new double[mrows];
    for( int i = 0; i < ncols; i++ )
    {
        for( int j = 0; j < mrows; j++ )
            v[j] = V[mrows * i + j];

        // Compute norm of the column vector
        double w = vec_2norm( mrows, v );

        if( fabs( w ) == 0 )
            ts[i] = 1;
        else
        {
            ts[i] = w;
            for( int j = 0; j < mrows; j++ )
                V[mrows * i + j] = V[mrows * i + j] / ts[i];
        }
    }
    delete[] v;
}

void DGMSolver::compute_qtransposeB( int mrows, int ncols, const double* Q, int bncols, double* bs )
{
    for( int k = 0; k < ncols; k++ )
    {
        for( int j = 0; j < bncols; j++ )
        {
            double t2 = 0;
            for( int i = k; i < mrows; i++ )
                t2 += Q[mrows * k + i] * bs[mrows * j + i];
            t2 = t2 + t2;

            for( int i = k; i < mrows; i++ )
                bs[mrows * j + i] -= t2 * Q[mrows * k + i];
        }
    }
}

void DGMSolver::qr_polyfit_safeguarded( const int mrows, const int ncols, double* V, double* D, int* rank )
{
    double tol = 1e-8;
    *rank      = ncols;
    double* v  = new double[mrows];

    for( int k = 0; k < ncols; k++ )
    {
        int nv = mrows - k;

        for( int j = 0; j < nv; j++ )
            v[j] = V[mrows * k + ( j + k )];

        double t2 = 0;

        for( int j = 0; j < nv; j++ )
            t2 = t2 + v[j] * v[j];

        double t    = sqrt( t2 );
        double vnrm = 0;

        if( v[0] >= 0 )
        {
            vnrm = sqrt( 2 * ( t2 + v[0] * t ) );
            v[0] = v[0] + t;
        }
        else
        {
            vnrm = sqrt( 2 * ( t2 - v[0] * t ) );
            v[0] = v[0] - t;
        }

        if( vnrm > 0 )
        {
            for( int j = 0; j < nv; j++ )
                v[j] = v[j] / vnrm;
        }

        for( int j = k; j < ncols; j++ )
        {
            t2 = 0;
            for( int i = 0; i < nv; i++ )
                t2 = t2 + v[i] * V[mrows * j + ( i + k )];

            t2 = t2 + t2;

            for( int i = 0; i < nv; i++ )
                V[mrows * j + ( i + k )] = V[mrows * j + ( i + k )] - t2 * v[i];
        }

        D[k] = V[mrows * k + k];

        for( int i = 0; i < nv; i++ )
            V[mrows * k + ( i + k )] = v[i];

        if( ( fabs( D[k] ) ) < tol && ( *rank == ncols ) )
        {
            *rank = k;
            break;
        }
    }

    delete[] v;
}

void DGMSolver::backsolve( int mrows, int ncols, double* R, int bncols, double* bs, double* ws )
{
#if 0
    std::cout.precision(16);
    std::cout<<"Before backsolve  "<<std::endl;
    std::cout<<" V = "<<std::endl;
    for (int k=0; k< ncols; k++){
        for (int j=0; j<mrows; ++j){
            std::cout<<R[mrows*k+j]<<std::endl;
          }
        std::cout<<std::endl;
      }
    std::cout<<std::endl;

    //std::cout<<"#pnts = "<<mrows<<std::endl;
    std::cout<<"bs = "<<std::endl;
    std::cout<<std::endl;
    for (int k=0; k< bncols; k++){
        for (int j=0; j<mrows; ++j){
            std::cout<<"  "<<bs[mrows*k+j]<<std::endl;
          }
      }
    std::cout<<std::endl;
#endif

    for( int k = 0; k < bncols; k++ )
    {
        for( int j = ncols - 1; j >= 0; j-- )
        {
            for( int i = j + 1; i < ncols; ++i )
                bs[mrows * k + j] = bs[mrows * k + j] - R[mrows * i + j] * bs[mrows * k + i];

            assert( R[mrows * j + j] != 0 );
            bs[mrows * k + j] = bs[mrows * k + j] / R[mrows * j + j];
        }
    }

    for( int k = 0; k < bncols; k++ )
    {
        for( int j = 0; j < ncols; ++j )
            bs[mrows * k + j] = bs[mrows * k + j] / ws[j];
    }
}

void DGMSolver::backsolve_polyfit_safeguarded( int dim,
                                               int degree,
                                               const bool interp,
                                               int mrows,
                                               int ncols,
                                               double* R,
                                               int bncols,
                                               double* bs,
                                               const double* ws,
                                               int* degree_out )
{
    if( ncols < 1 ) std::cout << "ERROR: Invalid input to safeguarded polyfit backsolve routine.\n";
#if 0
    std::cout.precision(12);
    std::cout<<"Before backsolve  "<<std::endl;
    std::cout<<" V = "<<std::endl;
    for (int k=0; k< ncols; k++){
        for (int j=0; j<mrows; ++j){
            std::cout<<R[mrows*k+j]<<std::endl;
          }
        std::cout<<std::endl;
      }
    std::cout<<std::endl;

    //std::cout<<"#pnts = "<<mrows<<std::endl;
    std::cout<<"bs = "<<std::endl;
    std::cout<<std::endl;
    for (int k=0; k< bncols; k++){
        for (int j=0; j<mrows; ++j){
            std::cout<<"  "<<bs[mrows*k+j]<<std::endl;
        }
    }
    std::cout<<std::endl;

    //std::cout<<" ] "<<std::endl;

    std::cout<<"Input ws = [ ";
    for (int k=0; k< ncols; k++){
            std::cout<<ws[k]<<", ";
          }
    std::cout<<" ] "<<std::endl;

    std::cout << "R: " << R << "size: [" << mrows << "," << ncols << "]" << std::endl;
    std::cout << "bs: " << bs << "size: [" << mrows << "," << bncols << "]" << std::endl;
    std::cout << "ws: " << ws << "size: [" << ncols << "," << 1 << "]" << std::endl;
    std::cout << "degree_out: " << degree_out << std::endl;
#endif

    int deg, numcols = 0;

    for( int k = 0; k < bncols; k++ )
    {
        deg = degree;
        /* I think we should consider interp = true/false -Xinglin*/
        if( dim == 1 )
            numcols = deg + 1 - interp;
        else if( dim == 2 )
            numcols = ( deg + 2 ) * ( deg + 1 ) / 2 - interp;

        assert( numcols <= ncols );

        std::vector< double > bs_bak( numcols );

        if( deg >= 2 )
        {
            for( int i = 0; i < numcols; i++ )
            {
                assert( mrows * k + i < mrows * bncols );
                bs_bak.at( i ) = bs[mrows * k + i];
            }
        }

        while( deg >= 1 )
        {
            int cend       = numcols - 1;
            bool downgrade = false;

            // The reconstruction can be applied only on edges (2-d) or faces (3-d)
            assert( cend >= 0 );
            assert( dim > 0 && dim < 3 );

            for( int d = deg; d >= 0; d-- )
            {
                int cstart = 0;
                if( dim == 1 )
                {
                    cstart = d;
                }
                else if( dim == 2 )
                {
                    cstart = ( ( d + 1 ) * d ) / 2;
                    // cstart = ((d*(d+1))>>1)-interp;
                }

                // Solve for  bs
                for( int j = cend; j >= cstart; j-- )
                {
                    assert( mrows * k + j < mrows * bncols );
                    for( int i = j + 1; i < numcols; ++i )
                    {
                        assert( mrows * k + i < mrows * bncols );
                        assert( mrows * i + j < mrows * ncols );  // check R
                        bs[mrows * k + j] = bs[mrows * k + j] - R[mrows * i + j] * bs[mrows * k + i];
                    }
                    assert( mrows * j + j < mrows * ncols );  // check R
                    bs[mrows * k + j] = bs[mrows * k + j] / R[mrows * j + j];
                }

                // Checking for change in the coefficient
                if( d >= 2 && d < deg )
                {
                    double tol;

                    if( dim == 1 )
                    {
                        tol = 1e-06;
                        assert( mrows * cstart + cstart < mrows * ncols );  // check R
                        double tb = bs_bak.at( cstart ) / R[mrows * cstart + cstart];
                        assert( mrows * k + cstart < mrows * bncols );
                        if( fabs( bs[mrows * k + cstart] - tb ) > ( 1 + tol ) * fabs( tb ) )
                        {
                            downgrade = true;
                            break;
                        }
                    }

                    else if( dim == 2 )
                    {
                        tol = 0.05;

                        std::vector< double > tb( cend - cstart + 1 );
                        for( int j = 0; j <= ( cend - cstart ); j++ )
                        {
                            tb.at( j ) = bs_bak.at( cstart + j );
                        }

                        for( int j = cend; j >= cstart; j-- )
                        {
                            int jind = j - cstart;

                            for( int i = j + 1; i <= cend; ++i )
                            {
                                assert( mrows * i + j < mrows * ncols );  // check R
                                tb.at( jind ) = tb.at( jind ) - R[mrows * i + j] * tb.at( i - cstart );
                            }
                            assert( mrows * j + j < mrows * ncols );  // check R
                            tb.at( jind ) = tb.at( jind ) / R[mrows * j + j];
                            assert( mrows * k + j < mrows * bncols );
                            double err = fabs( bs[mrows * k + j] - tb.at( jind ) );

                            if( ( err > tol ) && ( err >= ( 1 + tol ) * fabs( tb.at( jind ) ) ) )
                            {
                                downgrade = true;
                                break;
                            }
                        }

                        if( downgrade ) break;
                    }
                }

                cend = cstart - 1;
            }

            if( !downgrade )
                break;
            else
            {
                deg = deg - 1;
                if( dim == 1 )
                    numcols = deg + 1;
                else if( dim == 2 )
                    numcols = ( deg + 2 ) * ( deg + 1 ) / 2;

                for( int i = 0; i < numcols; i++ )
                {
                    assert( mrows * k + i < mrows * bncols );
                    bs[mrows * k + i] = bs_bak.at( i );
                }
            }
        }
        assert( k < bncols );
        degree_out[k] = deg;

        for( int i = 0; i < numcols; i++ )
        {
            // assert(mrows*k+i < mrows*bncols);
            // assert(i < ncols);
            bs[mrows * k + i] = bs[mrows * k + i] / ws[i];
        }

        for( int i = numcols; i < mrows; i++ )
        {
            // assert(mrows*k+i < mrows*bncols);
            bs[mrows * k + i] = 0;
        }
    }
}

void DGMSolver::vec_dotprod( const int len, const double* a, const double* b, double* c )
{
    if( !a || !b || !c )
    {
        MB_SET_ERR_RET( "NULL Pointer" );
    }
    for( int i = 0; i < len; ++i )
    {
        c[i] = a[i] * b[i];
    }
}

void DGMSolver::vec_scalarprod( const int len, const double* a, const double c, double* b )
{
    if( !a || !b )
    {
        MB_SET_ERR_RET( "NULL Pointer" );
    }
    for( int i = 0; i < len; ++i )
    {
        b[i] = c * a[i];
    }
}

void DGMSolver::vec_crossprod( const double a[3], const double b[3], double ( &c )[3] )
{
    c[0] = a[1] * b[2] - a[2] * b[1];
    c[1] = a[2] * b[0] - a[0] * b[2];
    c[2] = a[0] * b[1] - a[1] * b[0];
}

double DGMSolver::vec_innerprod( const int len, const double* a, const double* b )
{
    if( !a || !b )
    {
        MB_SET_ERR_RET_VAL( "NULL Pointer", 0.0 );
    }
    double ans = 0;
    for( int i = 0; i < len; ++i )
    {
        ans += a[i] * b[i];
    }
    return ans;
}

double DGMSolver::vec_2norm( const int len, const double* a )
{
    if( !a )
    {
        MB_SET_ERR_RET_VAL( "NULL Pointer", 0.0 );
    }
    double w = 0, s = 0;
    for( int k = 0; k < len; k++ )
        w = std::max( w, fabs( a[k] ) );

    if( w == 0 )
    {
        return 0;
    }
    else
    {
        for( int k = 0; k < len; k++ )
        {
            s += ( a[k] / w ) * ( a[k] / w );
        }
        s = w * sqrt( s );
    }
    return s;
}

double DGMSolver::vec_normalize( const int len, const double* a, double* b )
{
    if( !a || !b )
    {
        MB_SET_ERR_RET_VAL( "NULL Pointer", 0.0 );
    }
    double nrm = 0, mx = 0;
    for( int i = 0; i < len; ++i )
    {
        mx = std::max( fabs( a[i] ), mx );
    }
    if( mx == 0 )
    {
        for( int i = 0; i < len; ++i )
        {
            b[i] = 0;
        }
        return 0;
    }
    for( int i = 0; i < len; ++i )
    {
        nrm += ( a[i] / mx ) * ( a[i] / mx );
    }
    nrm = mx * sqrt( nrm );
    if( nrm == 0 )
    {
        return nrm;
    }
    for( int i = 0; i < len; ++i )
    {
        b[i] = a[i] / nrm;
    }
    return nrm;
}

double DGMSolver::vec_distance( const int len, const double* a, const double* b )
{
    double res = 0;
    for( int i = 0; i < len; ++i )
    {
        res += ( a[i] - b[i] ) * ( a[i] - b[i] );
    }
    return sqrt( res );
}

void DGMSolver::vec_projoff( const int len, const double* a, const double* b, double* c )
{
    if( !a || !b || !c )
    {
        MB_SET_ERR_RET( "NULL Pointer" );
    }
    // c = a-<a,b>b/<b,b>;
    double bnrm = vec_2norm( len, b );
    if( bnrm == 0 )
    {
        for( int i = 0; i < len; ++i )
        {
            c[i] = a[i];
        }
        return;
    }
    double innerp = vec_innerprod( len, a, b ) / bnrm;

    if( innerp == 0 )
    {
        if( c != a )
        {
            for( int i = 0; i < len; ++i )
            {
                c[i] = a[i];
            }
        }
        return;
    }

    for( int i = 0; i < len; ++i )
    {
        c[i] = a[i] - innerp * b[i] / bnrm;
    }
}

void DGMSolver::vec_linear_operation( const int len,
                                      const double mu,
                                      const double* a,
                                      const double psi,
                                      const double* b,
                                      double* c )
{
    if( !a || !b || !c )
    {
        MB_SET_ERR_RET( "NULL Pointer" );
    }
    for( int i = 0; i < len; ++i )
    {
        c[i] = mu * a[i] + psi * b[i];
    }
}

void DGMSolver::get_tri_natural_coords( const int dim,
                                        const double* cornercoords,
                                        const int npts,
                                        const double* currcoords,
                                        double* naturalcoords )
{
    assert( dim == 2 || dim == 3 );
    double a = 0, b = 0, d = 0, tol = 1e-12;
    for( int i = 0; i < dim; ++i )
    {
        a += ( cornercoords[dim + i] - cornercoords[i] ) * ( cornercoords[dim + i] - cornercoords[i] );
        b += ( cornercoords[dim + i] - cornercoords[i] ) * ( cornercoords[2 * dim + i] - cornercoords[i] );
        d += ( cornercoords[2 * dim + i] - cornercoords[i] ) * ( cornercoords[2 * dim + i] - cornercoords[i] );
    }
    double det = a * d - b * b;
    assert( det > 0 );
    for( int ipt = 0; ipt < npts; ++ipt )
    {
        double e = 0, f = 0;
        for( int i = 0; i < dim; ++i )
        {
            e += ( cornercoords[dim + i] - cornercoords[i] ) * ( currcoords[ipt * dim + i] - cornercoords[i] );
            f += ( cornercoords[2 * dim + i] - cornercoords[i] ) * ( currcoords[ipt * dim + i] - cornercoords[i] );
        }
        naturalcoords[ipt * 3 + 1] = ( e * d - b * f ) / det;
        naturalcoords[ipt * 3 + 2] = ( a * f - b * e ) / det;
        naturalcoords[ipt * 3]     = 1 - naturalcoords[ipt * 3 + 1] - naturalcoords[ipt * 3 + 2];
        if( naturalcoords[ipt * 3] < -tol || naturalcoords[ipt * 3 + 1] < -tol || naturalcoords[ipt * 3 + 2] < -tol )
        {
            std::cout << "Corners: \n";
            std::cout << cornercoords[0] << "\t" << cornercoords[1] << "\t" << cornercoords[3] << std::endl;
            std::cout << cornercoords[3] << "\t" << cornercoords[4] << "\t" << cornercoords[5] << std::endl;
            std::cout << cornercoords[6] << "\t" << cornercoords[7] << "\t" << cornercoords[8] << std::endl;
            std::cout << "Candidate: \n";
            std::cout << currcoords[ipt * dim] << "\t" << currcoords[ipt * dim + 1] << "\t" << currcoords[ipt * dim + 2]
                      << std::endl;
            exit( 0 );
        }
        assert( fabs( naturalcoords[ipt * 3] + naturalcoords[ipt * 3 + 1] + naturalcoords[ipt * 3 + 2] - 1 ) < tol );
        for( int i = 0; i < dim; ++i )
        {
            assert( fabs( naturalcoords[ipt * 3] * cornercoords[i] +
                          naturalcoords[ipt * 3 + 1] * cornercoords[dim + i] +
                          naturalcoords[ipt * 3 + 2] * cornercoords[2 * dim + i] - currcoords[ipt * dim + i] ) < tol );
        }
    }
}
}  // namespace moab