#ifndef FLENS_EXAMPLES_CG_BLAS_H
#define FLENS_EXAMPLES_CG_BLAS_H 1

#include <flens/flens.h>
#include <limits>

template <typename MA, typename VX, typename VB>
int
cg(const MA &A, const VB &b, VX &&x,
   double tol = std::numeric_limits<double>::epsilon(),
   int    maxIterations = std::numeric_limits<int>::max())
{
    using namespace flens;

    typedef typename VB::ElementType  ElementType;
    typedef typename VB::IndexType    IndexType;
    typedef typename VB::NoView       VectorType;

    ElementType  alpha, beta, rNormSquare, rNormSquarePrev;
    VectorType   Ap, r, p;

    const ElementType  Zero(0), One(1);

    blas::copy(b, r);
    blas::mv(NoTrans, -One, A, x, One, r);

    blas::copy(r, p);

    rNormSquare = blas::dot(r, r);

    for (int k=1; k<=maxIterations; ++k) {
        std::cout << "k = " << k << std::endl;
        if (sqrt(rNormSquare)<=tol) {
            return k-1;
        }

        blas::mv(NoTrans, One, A, p, Zero, Ap);

        alpha = rNormSquare/blas::dot(p, Ap);

        blas::axpy(alpha, p, x);

        blas::axpy(-alpha, Ap, r);

        rNormSquarePrev = rNormSquare;

        rNormSquare = blas::dot(r, r);

        beta = rNormSquare/rNormSquarePrev;

        blas::scal(beta, p);
        blas::axpy(One, r, p);
    }
    return maxIterations;
}

#endif // FLENS_EXAMPLES_CG_BLAS_H