matrixfunction.h

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#pragma once
#include <cmath>
 
#include <boost/math/special_functions.hpp> // has to be included before lapack in certain versions
#include "dg/algorithm.h"
 
#include "functors.h"
#include "sqrt_cauchy.h"
#include "sqrt_ode.h"
 
 
namespace dg {
namespace mat {
 
template<class UnaryOp>
auto make_FuncEigen_Te1( UnaryOp f)
{
    return [f]( const auto& T)
    {
        using value_type = typename std::decay_t<decltype(T)>::value_type;
        unsigned iter = T.O.size();
        thrust::host_vector<value_type> evals = T.O, plus  = T.P;
        thrust::host_vector<value_type> work (2*iter-2);
        dg::SquareMatrix<value_type> EHt(iter);
        //Compute Eigendecomposition
        lapack::stev(LAPACK_COL_MAJOR, 'V', evals, plus, EHt.data(), work);
        auto EH = EHt.transpose();
        //for( unsigned u=0; u<iter; u++)
        //    std::cout << u << " "<<evals[u]<<std::endl;
        //Compute f(T) e1 = E f(Lambda) E^t e1
        dg::HVec e1H(iter,0.), yH(e1H);
        e1H[0] = 1.;
        yH.resize( iter);
        dg::blas2::symv(EHt, e1H, yH);
        dg::blas1::transform(evals, e1H, [f] (double x){
            try{
                return f(x);
            }
            catch(boost::exception& e) //catch boost overflow error
            {
                return 0.;
            }
        });
        dg::blas1::pointwiseDot(e1H, yH, e1H);
        dg::blas2::symv(EH, e1H, yH);
        return yH;
    };
}
 
template< class value_type>
auto make_SqrtCauchy_Te1( int exp, std::array<value_type,2> EVs, unsigned stepsCauchy)
{
    return [=]( const auto& T)
    {
        unsigned size = T.O.size();
        thrust::host_vector<value_type> e1H(size, 0.), yH(e1H);
        e1H[0] = 1.;
 
        dg::mat::SqrtCauchyInt<HVec> cauchysqrtH( e1H);
        auto wTinv = [&w = cauchysqrtH.w(), &T = T]( const auto& y, auto& x)
        {
            // invert 1*T + w*wI
            dg::mat::compute_Tinv_y( T, x, y, 1., w*w);
        };
        cauchysqrtH(T, wTinv, e1H, yH, EVs, stepsCauchy, exp);
        return yH;
    };
}
 
template< class value_type>
auto make_SqrtCauchyEigen_Te1( int exp, std::array<value_type,2> EVs, unsigned stepsCauchy)
{
    std::function< value_type(value_type)> func = dg::SQRT<value_type>();
    if( exp < 0)
        func = [](value_type x){return 1./sqrt(x);};
 
    auto eigen = make_FuncEigen_Te1( func);
    auto cauchy = make_SqrtCauchy_Te1( exp, EVs, stepsCauchy);
    return [=]( const auto& T)
    {
        unsigned size = T.O.size();
        dg::HVec yH;
        if ( size < 40)
            yH = eigen( T);
        else
            yH = cauchy(T);
        return yH;
    };
}
 
 
template< class value_type>
auto make_SqrtODE_Te1( int exp, std::string tableau, value_type rtol,
        value_type atol, unsigned& number)
{
    return [=, &num = number](const auto& T)
    {
        unsigned size = T.O.size();
        HVec e1H(size, 0), yH(e1H);
        e1H[0] = 1.;
        auto inv_sqrt = make_inv_sqrtodeTri( T, e1H);
        auto sqrtHSolve =  make_directODESolve( inv_sqrt,
            tableau, rtol, atol, num);
        dg::apply( sqrtHSolve, e1H, yH);
        if( exp >= 0 )
        {
            dg::apply( T, yH, e1H);
            return e1H;
        }
        return yH;
    };
}
 
inline auto make_Linear_Te1( int exp)
{
    return [= ](const auto& T)
    {
        unsigned size = T.O.size();
        HVec e1H(size, 0), yH(e1H);
        e1H[0] = 1.;
        if( exp < 0)
            compute_Tinv_y( T, yH, e1H);
        else
            dg::blas2::symv( T, e1H, yH);
        return yH;
    };
}
 
} //namespace mat
} //namespace dg