src/operator/sequence_mask.cc

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

/*!
 * Copyright (c) 2015 by Contributors
 * \file sequence_mask.cc
 * \brief
 * \author Sebastian Bodenstein
*/
#include "./sequence_mask-inl.h"

namespace mxnet {
namespace op {
template <>
Operator *CreateOp<cpu>(SequenceMaskParam param, int dtype) {
  Operator *op = nullptr;
  MSHADOW_TYPE_SWITCH(dtype, DType,
                           { op = new SequenceMaskOp<cpu, DType>(param); })
  return op;
}

// DO_BIND_DISPATCH comes from operator_common.h
Operator *SequenceMaskProp::CreateOperatorEx(Context ctx,
                                             std::vector<TShape> *in_shape,
                                             std::vector<int> *in_type) const {
  DO_BIND_DISPATCH(CreateOp, param_, (*in_type)[0]);
}

DMLC_REGISTER_PARAMETER(SequenceMaskParam);

MXNET_REGISTER_OP_PROPERTY(SequenceMask, SequenceMaskProp)
    .describe(R"code(Sets all elements outside the sequence to a constant value.

This function takes an n-dimensional input array of the form
[max_sequence_length, batch_size, other_feature_dims] and returns an array of the same shape.

Parameter `sequence_length` is used to handle variable-length sequences. `sequence_length`
should be an input array of positive ints of dimension [batch_size].
To use this parameter, set `use_sequence_length` to `True`,
otherwise each example in the batch is assumed to have the max sequence length and
this operator works as the `identity` operator.

Example::

   x = [[[  1.,   2.,   3.],
         [  4.,   5.,   6.]],

        [[  7.,   8.,   9.],
         [ 10.,  11.,  12.]],

        [[ 13.,  14.,   15.],
         [ 16.,  17.,   18.]]]

   // Batch 1
   B1 = [[  1.,   2.,   3.],
         [  7.,   8.,   9.],
         [ 13.,  14.,  15.]]

   // Batch 2
   B2 = [[  4.,   5.,   6.],
         [ 10.,  11.,  12.],
         [ 16.,  17.,  18.]]

   // works as identity operator when sequence_length parameter is not used
   SequenceMask(x) = [[[  1.,   2.,   3.],
                       [  4.,   5.,   6.]],

                      [[  7.,   8.,   9.],
                       [ 10.,  11.,  12.]],

                      [[ 13.,  14.,   15.],
                       [ 16.,  17.,   18.]]]

   // sequence_length [1,1] means 1 of each batch will be kept
   // and other rows are masked with default mask value = 0
   SequenceMask(x, sequence_length=[1,1], use_sequence_length=True) =
                [[[  1.,   2.,   3.],
                  [  4.,   5.,   6.]],

                 [[  0.,   0.,   0.],
                  [  0.,   0.,   0.]],

                 [[  0.,   0.,   0.],
                  [  0.,   0.,   0.]]]

   // sequence_length [2,3] means 2 of batch B1 and 3 of batch B2 will be kept
   // and other rows are masked with value = 1
   SequenceMask(x, sequence_length=[2,3], use_sequence_length=True, value=1) =
                [[[  1.,   2.,   3.],
                  [  4.,   5.,   6.]],

                 [[  7.,   8.,   9.],
                  [  10.,  11.,  12.]],

                 [[   1.,   1.,   1.],
                  [  16.,  17.,  18.]]]

)code" ADD_FILELINE)
    .add_argument("data", "NDArray-or-Symbol",
                  "n-dimensional input array of the form [max_sequence_length,"
                  " batch_size, other_feature_dims] where n>2")
    .add_argument("sequence_length", "NDArray-or-Symbol",
                  "vector of sequence lengths of the form [batch_size]")
    .add_arguments(SequenceMaskParam::__FIELDS__());

}  // namespace op
}  // namespace mxnet