[onert] Introduce Optimizer (#11071)

This commit introduces Optimizer to be the base class of optimizers.

ONE-DCO-1.0-Signed-off-by: ragmani <ragmani0216@gmail.com>

runtime/onert/core/include/exec/train/optimizer/Optimizer.h

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2023 Samsung Electronics Co., Ltd. All Rights Reserved
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __ONERT_EXEC_TRAIN_OPTIMIZER_OPTIMIZER_H__
+#define __ONERT_EXEC_TRAIN_OPTIMIZER_OPTIMIZER_H__
+
+#include "backend/IPortableTensor.h"
+#include "backend/train/ITrainableTensor.h"
+
+#include <string>
+
+namespace onert
+{
+namespace exec
+{
+namespace train
+{
+namespace optimizer
+{
+
+// Gradient tensor, Trainable Tensor, Number of training steps
+using UpdateFactors =
+  std::tuple<const backend::IPortableTensor &, backend::train::ITrainableTensor &, size_t>;
+
+/**
+ * @class   Optimizer Base class for optimizers
+ * @brief   Base class for all optimizers
+ */
+class Optimizer
+{
+public:
+  virtual ~Optimizer() = default;
+
+  /**
+   * @brief Get the name of optimizer
+   *
+   * @return The name of optimizer
+   */
+  virtual std::string name() const { return std::string{"Invalid"}; }
+
+  /**
+   * @brief Get the Learning Rate
+   *
+   * @param iteration The number of training steps
+   * @return Learning rate
+   */
+  virtual double getLearningRate(uint32_t iteration) const = 0;
+
+  /**
+   * @brief Apply gradient to a trainable tensor
+   *
+   * @param factors UpdateFactors to be used for applying gradient to a trainable tensor
+   */
+  virtual void applyGradient(const UpdateFactors &factors) const = 0;
+
+  // TODO Add member functions for exporting optimizer information
+};
+
+} // namespace optimizer
+} // namespace train
+} // namespace exec
+} // namespace onert
+
+#endif // __ONERT_EXEC_TRAIN_OPTIMIZER_OPTIMIZER_H__