atomic_two Eigen Cholesky Factorization Class

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atomic_two_eigen_cholesky.hpp

@(@\newcommand{\W}[1]{ \; #1 \; } \newcommand{\R}[1]{ {\rm #1} } \newcommand{\B}[1]{ {\bf #1} } \newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} } \newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} } \newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} } \newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }@)@ This is cppad-20221105 documentation. Here is a link to its current documentation . atomic_two Eigen Cholesky Factorization Class
Purpose
Construct an atomic operation that computes a lower triangular matrix @(@ L @)@ such that @(@ L L^\R{T} = A @)@ for any positive integer @(@ p @)@ and symmetric positive definite matrix @(@ A \in \B{R}^{p \times p} @)@.

Start Class Definition

# include <cppad/cppad.hpp>
# include <Eigen/Dense>

Public

Types

namespace { // BEGIN_EMPTY_NAMESPACE

template <class Base>
class atomic_eigen_cholesky : public CppAD::atomic_base<Base> {
public:
    // -----------------------------------------------------------
    // type of elements during calculation of derivatives
    typedef Base              scalar;
    // type of elements during taping
    typedef CppAD::AD<scalar> ad_scalar;
    //
    // type of matrix during calculation of derivatives
    typedef Eigen::Matrix<
        scalar, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>        matrix;
    // type of matrix during taping
    typedef Eigen::Matrix<
        ad_scalar, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor > ad_matrix;
    //
    // lower triangular scalar matrix
    typedef Eigen::TriangularView<matrix, Eigen::Lower>             lower_view;

Constructor

    // constructor
    atomic_eigen_cholesky(void) : CppAD::atomic_base<Base>(
        "atom_eigen_cholesky"                             ,
        CppAD::atomic_base<Base>::set_sparsity_enum
    )
    { }

    // use atomic operation to invert an AD matrix
    ad_matrix op(const ad_matrix& arg)
    {   size_t nr = size_t( arg.rows() );
        size_t ny = ( (nr + 1 ) * nr ) / 2;
        size_t nx = 1 + ny;
        assert( nr == size_t( arg.cols() ) );
        // -------------------------------------------------------------------
        // packed version of arg
        CPPAD_TESTVECTOR(ad_scalar) packed_arg(nx);
        size_t index = 0;
        packed_arg[index++] = ad_scalar( nr );
        // lower triangle of symmetric matrix A
        for(size_t i = 0; i < nr; i++)
        {   for(size_t j = 0; j <= i; j++)
                packed_arg[index++] = arg( long(i), long(j) );
        }
        assert( index == nx );
        // -------------------------------------------------------------------
        // packed version of result = arg^{-1}.
        // This is an atomic_base function call that CppAD uses to
        // store the atomic operation on the tape.
        CPPAD_TESTVECTOR(ad_scalar) packed_result(ny);
        (*this)(packed_arg, packed_result);
        // -------------------------------------------------------------------
        // unpack result matrix L
        ad_matrix result = ad_matrix::Zero( long(nr), long(nr) );
        index = 0;
        for(size_t i = 0; i < nr; i++)
        {   for(size_t j = 0; j <= i; j++)
                result( long(i), long(j) ) = packed_result[index++];
        }
        return result;
    }

Private

Variables

private:
    // -------------------------------------------------------------
    // one forward mode vector of matrices for argument and result
    CppAD::vector<matrix> f_arg_, f_result_;
    // one reverse mode vector of matrices for argument and result
    CppAD::vector<matrix> r_arg_, r_result_;
    // -------------------------------------------------------------

forward

    // forward mode routine called by CppAD
    virtual bool forward(
        // lowest order Taylor coefficient we are evaluating
        size_t                          p ,
        // highest order Taylor coefficient we are evaluating
        size_t                          q ,
        // which components of x are variables
        const CppAD::vector<bool>&      vx ,
        // which components of y are variables
        CppAD::vector<bool>&            vy ,
        // tx [ j * (q+1) + k ] is x_j^k
        const CppAD::vector<scalar>&    tx ,
        // ty [ i * (q+1) + k ] is y_i^k
        CppAD::vector<scalar>&          ty
    )
    {   size_t n_order = q + 1;
        size_t nr      = size_t( CppAD::Integer( tx[ 0 * n_order + 0 ] ) );
        size_t ny      = ((nr + 1) * nr) / 2;
# ifndef NDEBUG
        size_t nx      = 1 + ny;
# endif
        assert( vx.size() == 0 || nx == vx.size() );
        assert( vx.size() == 0 || ny == vy.size() );
        assert( nx * n_order == tx.size() );
        assert( ny * n_order == ty.size() );
        //
        // -------------------------------------------------------------------
        // make sure f_arg_ and f_result_ are large enough
        assert( f_arg_.size() == f_result_.size() );
        if( f_arg_.size() < n_order )
        {   f_arg_.resize(n_order);
            f_result_.resize(n_order);
            //
            for(size_t k = 0; k < n_order; k++)
            {   f_arg_[k].resize( long(nr), long(nr) );
                f_result_[k].resize( long(nr), long(nr) );
            }
        }
        // -------------------------------------------------------------------
        // unpack tx into f_arg_
        for(size_t k = 0; k < n_order; k++)
        {   size_t index = 1;
            // unpack arg values for this order
            for(long i = 0; i < long(nr); i++)
            {   for(long j = 0; j <= i; j++)
                {   f_arg_[k](i, j) = tx[ index * n_order + k ];
                    f_arg_[k](j, i) = f_arg_[k](i, j);
                    index++;
                }
            }
        }
        // -------------------------------------------------------------------
        // result for each order
        // (we could avoid recalculting f_result_[k] for k=0,...,p-1)
        //
        Eigen::LLT<matrix> cholesky(f_arg_[0]);
        f_result_[0]   = cholesky.matrixL();
        lower_view L_0 = f_result_[0].template triangularView<Eigen::Lower>();
        for(size_t k = 1; k < n_order; k++)
        {   // initialize sum as A_k
            matrix f_sum = f_arg_[k];
            // compute A_k - B_k
            for(size_t ell = 1; ell < k; ell++)
                f_sum -= f_result_[ell] * f_result_[k-ell].transpose();
            // compute L_0^{-1} * (A_k - B_k) * L_0^{-T}
            matrix temp = L_0.template solve<Eigen::OnTheLeft>(f_sum);
            temp   = L_0.transpose().template solve<Eigen::OnTheRight>(temp);
            // divide the diagonal by 2
            for(long i = 0; i < long(nr); i++)
                temp(i, i) /= scalar(2.0);
            // L_k = L_0 * low[ L_0^{-1} * (A_k - B_k) * L_0^{-T} ]
            lower_view view = temp.template triangularView<Eigen::Lower>();
            f_result_[k] = f_result_[0] * view;
        }
        // -------------------------------------------------------------------
        // pack result_ into ty
        for(size_t k = 0; k < n_order; k++)
        {   size_t index = 0;
            for(long i = 0; i < long(nr); i++)
            {   for(long j = 0; j <= i; j++)
                {   ty[ index * n_order + k ] = f_result_[k](i, j);
                    index++;
                }
            }
        }
        // -------------------------------------------------------------------
        // check if we are computing vy
        if( vx.size() == 0 )
            return true;
        // ------------------------------------------------------------------
        // This is a very dumb algorithm that over estimates which
        // elements of the inverse are variables (which is not efficient).
        bool var = false;
        for(size_t i = 0; i < ny; i++)
            var |= vx[1 + i];
        for(size_t i = 0; i < ny; i++)
            vy[i] = var;
        //
        return true;
    }

reverse

    // reverse mode routine called by CppAD
    virtual bool reverse(
        // highest order Taylor coefficient that we are computing derivative of
        size_t                     q ,
        // forward mode Taylor coefficients for x variables
        const CppAD::vector<double>&     tx ,
        // forward mode Taylor coefficients for y variables
        const CppAD::vector<double>&     ty ,
        // upon return, derivative of G[ F[ {x_j^k} ] ] w.r.t {x_j^k}
        CppAD::vector<double>&           px ,
        // derivative of G[ {y_i^k} ] w.r.t. {y_i^k}
        const CppAD::vector<double>&     py
    )
    {   size_t n_order = q + 1;
        size_t nr = size_t( CppAD::Integer( tx[ 0 * n_order + 0 ] ) );
# ifndef NDEBUG
        size_t ny = ( (nr + 1 ) * nr ) / 2;
        size_t nx = 1 + ny;
# endif
        //
        assert( nx * n_order == tx.size() );
        assert( ny * n_order == ty.size() );
        assert( px.size()    == tx.size() );
        assert( py.size()    == ty.size() );
        // -------------------------------------------------------------------
        // make sure f_arg_ is large enough
        assert( f_arg_.size() == f_result_.size() );
        // must have previous run forward with order >= n_order
        assert( f_arg_.size() >= n_order );
        // -------------------------------------------------------------------
        // make sure r_arg_, r_result_ are large enough
        assert( r_arg_.size() == r_result_.size() );
        if( r_arg_.size() < n_order )
        {   r_arg_.resize(n_order);
            r_result_.resize(n_order);
            //
            for(size_t k = 0; k < n_order; k++)
            {   r_arg_[k].resize( long(nr), long(nr) );
                r_result_[k].resize( long(nr), long(nr) );
            }
        }
        // -------------------------------------------------------------------
        // unpack tx into f_arg_
        for(size_t k = 0; k < n_order; k++)
        {   size_t index = 1;
            // unpack arg values for this order
            for(long i = 0; i < long(nr); i++)
            {   for(long j = 0; j <= i; j++)
                {   f_arg_[k](i, j) = tx[ index * n_order + k ];
                    f_arg_[k](j, i) = f_arg_[k](i, j);
                    index++;
                }
            }
        }
        // -------------------------------------------------------------------
        // unpack py into r_result_
        for(size_t k = 0; k < n_order; k++)
        {   r_result_[k] = matrix::Zero( long(nr), long(nr) );
            size_t index = 0;
            for(long i = 0; i < long(nr); i++)
            {   for(long j = 0; j <= i; j++)
                {   r_result_[k](i, j) = py[ index * n_order + k ];
                    index++;
                }
            }
        }
        // -------------------------------------------------------------------
        // initialize r_arg_ as zero
        for(size_t k = 0; k < n_order; k++)
            r_arg_[k]   = matrix::Zero( long(nr), long(nr) );
        // -------------------------------------------------------------------
        // matrix reverse mode calculation
        lower_view L_0 = f_result_[0].template triangularView<Eigen::Lower>();
        //
        for(size_t k1 = n_order; k1 > 1; k1--)
        {   size_t k = k1 - 1;
            //
            // L_0^T * bar{L}_k
            matrix tmp1 = L_0.transpose() * r_result_[k];
            //
            //low[ L_0^T * bar{L}_k ]
            for(long i = 0; i < long(nr); i++)
                tmp1(i, i) /= scalar(2.0);
            matrix tmp2 = tmp1.template triangularView<Eigen::Lower>();
            //
            // L_0^{-T} low[ L_0^T * bar{L}_k ]
            tmp1 = L_0.transpose().template solve<Eigen::OnTheLeft>( tmp2 );
            //
            // M_k = L_0^{-T} * low[ L_0^T * bar{L}_k ]^{T} L_0^{-1}
            matrix M_k = L_0.transpose().template
                solve<Eigen::OnTheLeft>( tmp1.transpose() );
            //
            // remove L_k and compute bar{B}_k
            matrix barB_k = scalar(0.5) * ( M_k + M_k.transpose() );
            r_arg_[k]    += barB_k;
            barB_k        = scalar(-1.0) * barB_k;
            //
            // 2.0 * lower( bar{B}_k L_k )
            matrix temp = scalar(2.0) * barB_k * f_result_[k];
            temp        = temp.template triangularView<Eigen::Lower>();
            //
            // remove C_k
            r_result_[0] += temp;
            //
            // remove B_k
            for(size_t ell = 1; ell < k; ell++)
            {   // bar{L}_ell = 2 * lower( \bar{B}_k * L_{k-ell} )
                temp = scalar(2.0) * barB_k * f_result_[k-ell];
                r_result_[ell] += temp.template triangularView<Eigen::Lower>();
            }
        }
        // M_0 = L_0^{-T} * low[ L_0^T * bar{L}_0 ]^{T} L_0^{-1}
        matrix M_0 = L_0.transpose() * r_result_[0];
        for(long i = 0; i < long(nr); i++)
            M_0(i, i) /= scalar(2.0);
        M_0 = M_0.template triangularView<Eigen::Lower>();
        M_0 = L_0.template solve<Eigen::OnTheRight>( M_0 );
        M_0 = L_0.transpose().template solve<Eigen::OnTheLeft>( M_0 );
        // remove L_0
        r_arg_[0] += scalar(0.5) * ( M_0 + M_0.transpose() );
        // -------------------------------------------------------------------
        // pack r_arg into px
        // note that only the lower triangle of barA_k is stored in px
        for(size_t k = 0; k < n_order; k++)
        {   size_t index = 0;
            px[ index * n_order + k ] = 0.0;
            index++;
            for(long i = 0; i < long(nr); i++)
            {   for(long j = 0; j < i; j++)
                {   px[ index * n_order + k ] = 2.0 * r_arg_[k](i, j);
                    index++;
                }
                px[ index * n_order + k] = r_arg_[k](i, i);
                index++;
            }
        }
        // -------------------------------------------------------------------
        return true;
    }

End Class Definition


}; // End of atomic_eigen_cholesky class

}  // END_EMPTY_NAMESPACE

Input File: include/cppad/example/atomic_two/eigen_cholesky.hpp