/**
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* @license
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* Copyright 2021 Google LLC. All Rights Reserved.
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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* =============================================================================
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*/
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/// <amd-module name="@tensorflow/tfjs-core/dist/ops/einsum" />
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import { Tensor } from '../tensor';
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/**
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* Tensor contraction over specified indices and outer product.
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*
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* `einsum` allows defining Tensors by defining their element-wise computation.
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* This computation is based on
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* [Einstein summation](https://en.wikipedia.org/wiki/Einstein_notation).
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*
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* Some special cases include:
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*
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* Matrix multiplication:
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* ```js
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* const x = tf.tensor2d([[1, 2, 3], [4, 5, 6]]);
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* const y = tf.tensor2d([[0, 1], [2, 3], [4, 5]]);
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* x.print();
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* y.print();
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* tf.einsum('ij,jk->ik', x, y).print();
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* ```
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*
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* Dot product:
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* ```js
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* const x = tf.tensor1d([1, 2, 3]);
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* const y = tf.tensor1d([0, 1, 2]);
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* x.print();
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* y.print();
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* tf.einsum('i,i->', x, y).print();
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* ```
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*
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* Batch dot product:
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* ```js
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* const x = tf.tensor2d([[1, 2, 3], [4, 5, 6]]);
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* const y = tf.tensor2d([[0, 1, 2], [3, 4, 5]]);
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* x.print();
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* y.print();
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* tf.einsum('bi,bi->b', x, y).print();
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* ```
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*
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* Outer prouduct:
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* ```js
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* const x = tf.tensor1d([1, 3, 5]);
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* const y = tf.tensor1d([2, 4, 6]);
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* x.print();
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* y.print();
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* tf.einsum('i,j->ij', x, y).print();
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* ```
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*
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* Matrix transpose:
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* ```js
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* const x = tf.tensor2d([[1, 2], [3, 4]]);
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* x.print();
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* tf.einsum('ij->ji', x).print();
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* ```
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*
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* Batch matrix transpose:
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* ```js
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* const x = tf.tensor3d([[[1, 2], [3, 4]], [[-1, -2], [-3, -4]]]);
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* x.print();
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* tf.einsum('bij->bji', x).print();
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* ```
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*
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* Limitations:
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*
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* This implementation of einsum has the following limitations:
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*
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* - Does not support >2 input tensors.
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* - Does not support duplicate axes for any given input tensor. E.g., equation
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* 'ii->' is not supported.
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* - The `...` notation is not supported.
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*
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* @param equation a string describing the contraction, in the same format as
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* [numpy.einsum](https://numpy.org/doc/stable/reference/generated/numpy.einsum.html).
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* @param tensors the input(s) to contract (each one a Tensor), whose shapes
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* should be consistent with equation.
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* @returns The output tensor.
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*
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* @doc {heading: 'Tensors', subheading: 'Matrices'}
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*/
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export declare function einsum_(equation: string, ...tensors: Tensor[]): Tensor;
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export declare const einsum: typeof einsum_;
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