identity.hpp

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// SPDX-License-Identifier: BSD-2-Clause
 
#ifndef pRC_TENSOR_TRAIN_OPERATOR_IDENTITY_H
#define pRC_TENSOR_TRAIN_OPERATOR_IDENTITY_H
 
#include <prc/core/basic/functions/identity.hpp>
#include <prc/core/functors/direct_sum.hpp>
#include <prc/core/functors/eval.hpp>
#include <prc/tensor_train/operator/views/enumerate.hpp>
 
namespace pRC
{
    template<TensorTrain::IsOperator T>
    struct Identity<T>
    {
        constexpr auto operator()() const
        {
            auto const f = []<Index C>()
            {
                using Core = typename T::template Cores<C>;
                constexpr auto CRL = Core::size(0);
                constexpr auto CM = Core::size(1);
                constexpr auto CN = Core::size(2);
                constexpr auto CRR = Core::size(3);
 
                return permute<2, 0, 1, 3>(exclude<DirectSum, 1, 2>(
                    reshape<1, CM, CN, 1>(identity<
                        typename Core::template ChangeSizes<CM, CN>>()),
                    zero<typename Core::template ChangeSizes<CRL - 1, CM, CN,
                        CRR - 1>>()));
            };
 
            using F = RemoveConstReference<decltype(f)>;
            using M = typename T::M;
            using N = typename T::N;
            using Ranks = typename T::Ranks;
 
            return TensorTrain::OperatorViews::Enumerate<typename T::Type, M, N,
                Ranks, F>(f);
        }
 
        template<class X>
            requires IsConstructible<typename T::Type, X>
        constexpr auto operator()(X &&value) const
        {
            auto const f =
                [value = typename T::Type(forward<X>(value))]<Index C>()
            {
                using Core = typename T::template Cores<C>;
                constexpr auto CRL = Core::size(0);
                constexpr auto CM = Core::size(1);
                constexpr auto CN = Core::size(2);
                constexpr auto CRR = Core::size(3);
 
                if constexpr(C == 0)
                {
                    return permute<2, 0, 1, 3>(exclude<DirectSum, 1, 2>(
                        reshape<1, CM, CN, 1>(identity<
                            typename Core::template ChangeSizes<CM, CN>>(
                            value)),
                        zero<typename Core::template ChangeSizes<CRL - 1, CM,
                            CN, CRR - 1>>()));
                }
                else
                {
                    return permute<2, 0, 1, 3>(exclude<DirectSum, 1, 2>(
                        reshape<1, CM, CN, 1>(identity<
                            typename Core::template ChangeSizes<CM, CN>>()),
                        zero<typename Core::template ChangeSizes<CRL - 1, CM,
                            CN, CRR - 1>>()));
                }
            };
 
            using F = RemoveConstReference<decltype(f)>;
            using M = typename T::M;
            using N = typename T::N;
            using Ranks = typename T::Ranks;
 
            return TensorTrain::OperatorViews::Enumerate<typename T::Type, M, N,
                Ranks, F>(f);
        }
    };
 
    template<TensorTrain::IsOperatorView T>
    struct Identity<T> : Identity<ResultOf<Eval, T>>
    {
    };
}
#endif // pRC_TENSOR_TRAIN_OPERATOR_IDENTITY_H