#ifndef STAN_MATH_PRIM_MAT_FUN_TRACE_INV_QUAD_FORM_LDLT_HPP
#define STAN_MATH_PRIM_MAT_FUN_TRACE_INV_QUAD_FORM_LDLT_HPP

#include <stan/math/prim/mat/fun/Eigen.hpp>
#include <stan/math/prim/mat/fun/LDLT_factor.hpp>
#include <stan/math/prim/mat/err/check_multiplicable.hpp>
#include <stan/math/prim/mat/fun/mdivide_left_ldlt.hpp>
#include <stan/math/prim/mat/fun/trace.hpp>
#include <stan/math/prim/mat/fun/transpose.hpp>
#include <stan/math/prim/mat/fun/multiply.hpp>
#include <stan/math/prim/scal/meta/is_var.hpp>

namespace stan {
  namespace math {

    /*
     * Compute the trace of an inverse quadratic form.  I.E., this computes
     *       trace(B^T A^-1 B)
     * where the LDLT_factor of A is provided.
     */
    template <typename T1, typename T2, int R2, int C2, int R3, int C3>
    inline typename
    boost::enable_if_c<!stan::is_var<T1>::value &&
                       !stan::is_var<T2>::value,
                       typename
                       boost::math::tools::promote_args<T1, T2>::type>::type
    trace_inv_quad_form_ldlt(const stan::math::LDLT_factor<T1, R2, C2> &A,
                             const Eigen::Matrix<T2, R3, C3> &B) {
      stan::math::check_multiplicable("trace_inv_quad_form_ldlt",
                                                "A", A,
                                                "B", B);

      return trace(multiply(transpose(B), mdivide_left_ldlt(A, B)));
    }
  }
}

#endif
