backwards.hpp

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// SPDX-License-Identifier: BSD-2-Clause
 
#ifndef pRC_TENSOR_TRAIN_OPERATOR_FUNCTIONS_BACKWARDS_H
#define pRC_TENSOR_TRAIN_OPERATOR_FUNCTIONS_BACKWARDS_H
 
#include <prc/core/functors/view.hpp>
#include <prc/tensor_train/operator/views/backwards.hpp>
 
namespace pRC
{
    template<class X, TensorTrain::IsOperatorish R = RemoveReference<X>>
    static inline constexpr auto backwards(X &&a)
    {
        if constexpr(IsInvocable<View, X>)
        {
            using V = RemoveReference<decltype(view(forward<X>(a)))>;
            using M = decltype(reverse(typename R::M()));
            using N = decltype(reverse(typename R::N()));
            using Ranks = decltype(reverse(typename R::Ranks()));
 
            return TensorTrain::OperatorViews::Backwards<typename R::Type, M, N,
                Ranks, V>(view(forward<X>(a)));
        }
        else
        {
            return eval(backwards(a));
        }
    }
}
#endif // pRC_TENSOR_TRAIN_OPERATOR_FUNCTIONS_BACKWARDS_H