Merge branch 'develop' of https://github.com/baidu/Paddle into inference
hedaoyuan
8 years ago
commit
cad7bd13d2
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# Benchmark
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Machine:
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- Server
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- Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz, 2 Sockets, 20 Cores per socket
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- Laptop
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- DELL XPS15-9560-R1745: i7-7700HQ 8G 256GSSD
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- i5 MacBook Pro (Retina, 13-inch, Early 2015)
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- Desktop
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- i7-6700k
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System: CentOS release 6.3 (Final), Docker 1.12.1.
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PaddlePaddle: paddlepaddle/paddle:latest (TODO: will rerun after 0.11.0)
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- MKL-DNN tag v0.10
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- MKLML 2018.0.20170720
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- OpenBLAS v0.2.20
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On each machine, we will test and compare the performance of training on single node using MKL-DNN / MKLML / OpenBLAS respectively.
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## Benchmark Model
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### Server
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Test on batch size 64, 128, 256 on Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz
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Input image size - 3 * 224 * 224, Time: images/second
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- VGG-19
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| BatchSize | 64 | 128 | 256 |
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|--------------|-------| -----| --------|
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| OpenBLAS | 7.82 | 8.62 | 10.34 |
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| MKLML | 11.02 | 12.86 | 15.33 |
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| MKL-DNN | 27.69 | 28.8 | 29.27 |
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chart on batch size 128
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TBD
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- ResNet
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- GoogLeNet
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### Laptop
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TBD
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### Desktop
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TBD
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@ -0,0 +1,213 @@
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#!/usr/bin/env python
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from paddle.trainer_config_helpers import *
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height = 224
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width = 224
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num_class = 1000
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batch_size = get_config_arg('batch_size', int, 64)
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layer_num = get_config_arg("layer_num", int, 50)
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is_test = get_config_arg("is_test", bool, False)
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args = {'height': height, 'width': width, 'color': True, 'num_class': num_class}
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define_py_data_sources2(
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"train.list", None, module="provider", obj="process", args=args)
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settings(
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batch_size=batch_size,
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learning_rate=0.01 / batch_size,
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learning_method=MomentumOptimizer(0.9),
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regularization=L2Regularization(0.0005 * batch_size))
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#######################Network Configuration #############
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def conv_bn_layer(name,
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input,
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filter_size,
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num_filters,
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stride,
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padding,
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channels=None,
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active_type=ReluActivation()):
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"""
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A wrapper for conv layer with batch normalization layers.
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Note:
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conv layer has no activation.
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"""
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tmp = img_conv_layer(
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name=name + "_conv",
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input=input,
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filter_size=filter_size,
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num_channels=channels,
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num_filters=num_filters,
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stride=stride,
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padding=padding,
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act=LinearActivation(),
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bias_attr=False)
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return batch_norm_layer(
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name=name + "_bn", input=tmp, act=active_type, use_global_stats=is_test)
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def bottleneck_block(name, input, num_filters1, num_filters2):
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"""
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A wrapper for bottlenect building block in ResNet.
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Last conv_bn_layer has no activation.
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Addto layer has activation of relu.
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"""
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last_name = conv_bn_layer(
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name=name + '_branch2a',
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input=input,
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filter_size=1,
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num_filters=num_filters1,
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stride=1,
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padding=0)
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last_name = conv_bn_layer(
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name=name + '_branch2b',
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input=last_name,
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filter_size=3,
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num_filters=num_filters1,
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stride=1,
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padding=1)
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last_name = conv_bn_layer(
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name=name + '_branch2c',
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input=last_name,
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filter_size=1,
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num_filters=num_filters2,
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stride=1,
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padding=0,
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active_type=LinearActivation())
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return addto_layer(
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name=name + "_addto", input=[input, last_name], act=ReluActivation())
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def mid_projection(name, input, num_filters1, num_filters2, stride=2):
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"""
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A wrapper for middile projection in ResNet.
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projection shortcuts are used for increasing dimensions,
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and other shortcuts are identity
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branch1: projection shortcuts are used for increasing
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dimensions, has no activation.
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branch2x: bottleneck building block, shortcuts are identity.
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"""
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# stride = 2
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branch1 = conv_bn_layer(
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name=name + '_branch1',
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input=input,
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filter_size=1,
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num_filters=num_filters2,
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stride=stride,
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padding=0,
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active_type=LinearActivation())
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|
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last_name = conv_bn_layer(
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name=name + '_branch2a',
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input=input,
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filter_size=1,
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num_filters=num_filters1,
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stride=stride,
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padding=0)
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last_name = conv_bn_layer(
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name=name + '_branch2b',
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input=last_name,
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filter_size=3,
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num_filters=num_filters1,
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stride=1,
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padding=1)
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|
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last_name = conv_bn_layer(
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name=name + '_branch2c',
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input=last_name,
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filter_size=1,
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num_filters=num_filters2,
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stride=1,
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padding=0,
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active_type=LinearActivation())
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return addto_layer(
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name=name + "_addto", input=[branch1, last_name], act=ReluActivation())
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img = data_layer(name='image', size=height * width * 3)
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def deep_res_net(res2_num=3, res3_num=4, res4_num=6, res5_num=3):
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"""
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A wrapper for 50,101,152 layers of ResNet.
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res2_num: number of blocks stacked in conv2_x
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res3_num: number of blocks stacked in conv3_x
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res4_num: number of blocks stacked in conv4_x
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res5_num: number of blocks stacked in conv5_x
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"""
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# For ImageNet
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# conv1: 112x112
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tmp = conv_bn_layer(
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"conv1",
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input=img,
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filter_size=7,
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channels=3,
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num_filters=64,
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stride=2,
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padding=3)
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tmp = img_pool_layer(name="pool1", input=tmp, pool_size=3, stride=2)
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# conv2_x: 56x56
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tmp = mid_projection(
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name="res2_1", input=tmp, num_filters1=64, num_filters2=256, stride=1)
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for i in xrange(2, res2_num + 1, 1):
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tmp = bottleneck_block(
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name="res2_" + str(i), input=tmp, num_filters1=64, num_filters2=256)
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# conv3_x: 28x28
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tmp = mid_projection(
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name="res3_1", input=tmp, num_filters1=128, num_filters2=512)
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for i in xrange(2, res3_num + 1, 1):
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tmp = bottleneck_block(
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name="res3_" + str(i),
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input=tmp,
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num_filters1=128,
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num_filters2=512)
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# conv4_x: 14x14
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tmp = mid_projection(
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name="res4_1", input=tmp, num_filters1=256, num_filters2=1024)
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for i in xrange(2, res4_num + 1, 1):
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tmp = bottleneck_block(
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name="res4_" + str(i),
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input=tmp,
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num_filters1=256,
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num_filters2=1024)
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# conv5_x: 7x7
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tmp = mid_projection(
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name="res5_1", input=tmp, num_filters1=512, num_filters2=2048)
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for i in xrange(2, res5_num + 1, 1):
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tmp = bottleneck_block(
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name="res5_" + str(i),
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input=tmp,
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num_filters1=512,
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num_filters2=2048)
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tmp = img_pool_layer(
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name='avgpool',
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input=tmp,
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pool_size=7,
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stride=1,
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pool_type=AvgPooling())
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return fc_layer(input=tmp, size=num_class, act=SoftmaxActivation())
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if layer_num == 50:
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resnet = deep_res_net(3, 4, 6, 3)
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elif layer_num == 101:
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resnet = deep_res_net(3, 4, 23, 3)
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elif layer_num == 152:
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resnet = deep_res_net(3, 8, 36, 3)
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else:
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print("Wrong layer number.")
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lbl = data_layer(name="label", size=num_class)
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loss = cross_entropy(name='loss', input=resnet, label=lbl)
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inputs(img, lbl)
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outputs(loss)
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@ -0,0 +1,36 @@
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=====================
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Data Reader Interface
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=====================
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DataTypes
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=========
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.. automodule:: paddle.v2.data_type
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:members:
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:noindex:
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DataFeeder
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==========
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.. automodule:: paddle.v2.data_feeder
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:members:
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:noindex:
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Reader
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======
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.. automodule:: paddle.v2.reader
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:members:
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:noindex:
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|
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.. automodule:: paddle.v2.reader.creator
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:members:
|
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:noindex:
|
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|
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minibatch
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||||
=========
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||||
|
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.. automodule:: paddle.v2.minibatch
|
||||
:members:
|
||||
:noindex:
|
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@ -0,0 +1,75 @@
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Dataset
|
||||
=======
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||||
|
||||
.. automodule:: paddle.v2.dataset
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:members:
|
||||
:noindex:
|
||||
|
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mnist
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+++++
|
||||
|
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.. automodule:: paddle.v2.dataset.mnist
|
||||
:members:
|
||||
:noindex:
|
||||
|
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cifar
|
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+++++
|
||||
|
||||
.. automodule:: paddle.v2.dataset.cifar
|
||||
:members:
|
||||
:noindex:
|
||||
|
||||
conll05
|
||||
+++++++
|
||||
|
||||
.. automodule:: paddle.v2.dataset.conll05
|
||||
:members: get_dict,get_embedding,test
|
||||
:noindex:
|
||||
|
||||
imdb
|
||||
++++
|
||||
|
||||
.. automodule:: paddle.v2.dataset.imdb
|
||||
:members:
|
||||
:noindex:
|
||||
|
||||
imikolov
|
||||
++++++++
|
||||
|
||||
.. automodule:: paddle.v2.dataset.imikolov
|
||||
:members:
|
||||
:noindex:
|
||||
|
||||
movielens
|
||||
+++++++++
|
||||
|
||||
.. automodule:: paddle.v2.dataset.movielens
|
||||
:members:
|
||||
:noindex:
|
||||
|
||||
.. autoclass:: paddle.v2.dataset.movielens.MovieInfo
|
||||
:noindex:
|
||||
|
||||
.. autoclass:: paddle.v2.dataset.movielens.UserInfo
|
||||
:noindex:
|
||||
|
||||
sentiment
|
||||
+++++++++
|
||||
|
||||
.. automodule:: paddle.v2.dataset.sentiment
|
||||
:members:
|
||||
:noindex:
|
||||
|
||||
uci_housing
|
||||
+++++++++++
|
||||
|
||||
.. automodule:: paddle.v2.dataset.uci_housing
|
||||
:members:
|
||||
:noindex:
|
||||
|
||||
wmt14
|
||||
+++++
|
||||
|
||||
.. automodule:: paddle.v2.dataset.wmt14
|
||||
:members:
|
||||
:noindex:
|
||||
@ -0,0 +1,5 @@
|
||||
Image Interface
|
||||
===============
|
||||
|
||||
.. automodule:: paddle.v2.image
|
||||
:members:
|
||||
@ -0,0 +1,60 @@
|
||||
# Design Doc: float16
|
||||
|
||||
## Why float16
|
||||
Half precision (float16) is a binary floating-point format that occupies 16 bits in memory. float16 is half the size of traditional 32-bit single precision format (float) and has lower precision and smaller range.
|
||||
|
||||
When high precision computation is not required, using float16 data type could potentially
|
||||
|
||||
- reduce storage space, memory bandwidth, and power usages;
|
||||
- increase the chance of data fitting into a smaller cache of lower latency;
|
||||
- provide arithmetic speed up if supported by hardware.
|
||||
|
||||
## Survey of current float16 support
|
||||
A brief survey of float16 support on different compilers, hardwares, and libraries can be found below. Interested readers can refer to [link1](https://github.com/PaddlePaddle/Paddle/issues/4853) and [link2](https://github.com/Xreki/Xreki.github.io/blob/master/multi_data_types_in_dl_framework/ppt/float16_and_quantized_type.md) for more info.
|
||||
|
||||
The goal of float16 is to serve as a key for the executor to find and run the correct version of compute method specialized for float16 in operator kernel. It should be compatible with various natively supported float16 implementations including `__half` for cuda, `float16_t` for ARM, and `Eigen::half` for Eigen to make writing customized float16 kernels easier.
|
||||
|
||||
### Compiler
|
||||
- nvcc supports `__half` data type after CUDA 7.5.
|
||||
- `__fp16` or `float16_t` is supported as storage type for gcc >= 6.1 and clang >= 3.4.
|
||||
- `__fp16` or `float16_t` is supported as arithmetic type for gcc >= 7.1 and clang >= 3.9.
|
||||
|
||||
### Hardware
|
||||
- `__half` is supported on GPU with compute capability >= 5.3.
|
||||
- `__fp16` is supported as storage type for ARMv7-A, ARMv8-A, and above.
|
||||
- `__fp16` is supported as arithmetic type after ARMv8.2-A (currently, the only microarchitecture implementing ARMv8.2-A is ARM Cortex-A75, which is announced in May 2017. There seems to be no application processors currently available on market that adopts this architecture. It is reported that Qualcomm Snapdragon 845 uses Cortex-A75 design and will be available in mobile devices in early 2018).
|
||||
|
||||
### Libraries
|
||||
- [Eigen](https://github.com/RLovelett/eigen) >= 3.3 supports float16 calculation on both GPU and CPU using the `Eigen::half` class. It is mostly useful for Nvidia GPUs because of the overloaded arithmetic operators using cuda intrinsics. It falls back to using software emulation on CPU for calculation and there is no special treatment to ARM processors.
|
||||
- [ARM compute library](https://github.com/ARM-software/ComputeLibrary) >= 17.02.01 supports NEON FP16 kernels (requires ARMv8.2-A CPU).
|
||||
|
||||
|
||||
## Implementation
|
||||
The float16 class holds a 16-bit `uint16_t` data internally.
|
||||
```
|
||||
struct float16 {
|
||||
uint16_t x;
|
||||
};
|
||||
```
|
||||
|
||||
float16 supports the following features:
|
||||
- constructors / assignment operators that take input from primitive data types including bool, integers of various length, float, and double.
|
||||
- constructors / assignment operators that take input from `__half` on cuda, `float16_t` on ARM, and `Eigen::half` on Eigen.
|
||||
- conversion operators to primitive data types and half precision data types on cuda, ARM and Eigen.
|
||||
- overloaded arithmetic operators for cuda, arm, and non-arm cpu, respectively. These operators will take advantage of the cuda and ARM intrinsics on the corresponding hardware.
|
||||
|
||||
To support the above features, two fundamental conversion functions are provided:
|
||||
```
|
||||
float16 float_to_half_rn(float f); // convert to half precision in round-to-nearest-even mode
|
||||
float half_to_float(float16 h);
|
||||
```
|
||||
which provides one-to-one conversion between float32 and float16. These twos functions will do different conversion routines based on the current hardware. CUDA/ARM instrinsics will be used when the corresonding hardware is available. If the hardware or compiler level does not support float32 to float16 conversion, software emulation will be performed to do the conversion.
|
||||
|
||||
## To do
|
||||
After float16 class is available, some of the future items are below:
|
||||
|
||||
- Update pybind/tensor_py.h to bind c++ float16 with numpy float16.
|
||||
|
||||
- Modify `GetKernelType()` method in `framework/operator.h` to make it compatible with float16.
|
||||
|
||||
- Create a type-casting operator that can convert the data type in tensor between float16 and other types.
|
||||
|
After Width: | Height: | Size: 620 B |
|
After Width: | Height: | Size: 156 B |
|
After Width: | Height: | Size: 61 KiB |
@ -0,0 +1,245 @@
|
||||
# Design: Sequence Decoder Generating LoDTensors
|
||||
In tasks such as machine translation and image to text,
|
||||
a [sequence decoder](https://github.com/PaddlePaddle/book/blob/develop/08.machine_translation/README.md) is necessary to generate sequences.
|
||||
|
||||
This documentation describes how to implement the sequence decoder as an operator.
|
||||
|
||||
## Beam Search based Decoder
|
||||
The [beam search algorithm](https://en.wikipedia.org/wiki/Beam_search) is necessary when generating sequences,
|
||||
it is a heuristic search algorithm that explores the paths by expanding the most promising node in a limited set.
|
||||
|
||||
In the old version of PaddlePaddle, a C++ class `RecurrentGradientMachine` implements the general sequence decoder based on beam search,
|
||||
due to the complexity, the implementation relays on a lot of special data structures,
|
||||
quite trivial and hard to be customized by users.
|
||||
|
||||
There are a lot of heuristic tricks in the sequence generation tasks,
|
||||
so the flexibility of sequence decoder is very important to users.
|
||||
|
||||
During PaddlePaddle's refactoring work,
|
||||
some new concept is proposed such as [LoDTensor](https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/framework/lod_tensor.md) and [TensorArray](https://github.com/PaddlePaddle/Paddle/blob/develop/doc/design/tensor_array.md) that can better support sequence usage,
|
||||
and they can help to make the implementation of beam search based sequence decoder **more transparent and modular** .
|
||||
|
||||
For example, the RNN sates, candidates IDs and probabilities of beam search can be represented as `LoDTensors`;
|
||||
the selected candidate's IDs in each time step can be stored in a `TensorArray`, and `Packed` to the sentences translated.
|
||||
|
||||
## Changing LoD's absolute offset to relative offsets
|
||||
The current `LoDTensor` is designed to store levels of variable-length sequences,
|
||||
it stores several arrays of integers each represents a level.
|
||||
|
||||
The integers in each level represents the begin and end (not inclusive) offset of a sequence **in the underlying tensor**,
|
||||
let's call this format the **absolute-offset LoD** for clear.
|
||||
|
||||
The relative-offset LoD can fast retrieve any sequence but fails to represent empty sequences, for example, a two-level LoD is as follows
|
||||
```python
|
||||
[[0, 3, 9]
|
||||
[0, 2, 3, 3, 3, 9]]
|
||||
```
|
||||
The first level tells that there are two sequences:
|
||||
- the first's offset is `[0, 3)`
|
||||
- the second's offset is `[3, 9)`
|
||||
|
||||
while on the second level, there are several empty sequences that both begin and end at `3`.
|
||||
It is impossible to tell how many empty second-level sequences exist in the first-level sequences.
|
||||
|
||||
There are many scenarios that relay on empty sequence representation,
|
||||
such as machine translation or image to text, one instance has no translations or the empty candidate set for a prefix.
|
||||
|
||||
So let's introduce another format of LoD,
|
||||
it stores **the offsets of the lower level sequences** and is called **relative-offset** LoD.
|
||||
|
||||
For example, to represent the same sequences of the above data
|
||||
|
||||
```python
|
||||
[[0, 3, 6]
|
||||
[0, 2, 3, 3, 3, 9]]
|
||||
```
|
||||
|
||||
the first level represents that there are two sequences,
|
||||
their offsets in the second-level LoD is `[0, 3)` and `[3, 5)`.
|
||||
|
||||
The second level is the same with the relative offset example because the lower level is a tensor.
|
||||
It is easy to find out the second sequence in the first-level LoD has two empty sequences.
|
||||
|
||||
The following demos are based on relative-offset LoD.
|
||||
|
||||
## Usage in a simple machine translation model
|
||||
Let's start from a simple machine translation model that is simplified from [machine translation chapter](https://github.com/PaddlePaddle/book/tree/develop/08.machine_translation) to draw a simple blueprint of what a sequence decoder can do and how to use it.
|
||||
|
||||
The model has an encoder that learns the semantic vector from a sequence,
|
||||
and a decoder which uses the sequence decoder to generate new sentences.
|
||||
|
||||
**Encoder**
|
||||
```python
|
||||
import paddle as pd
|
||||
|
||||
dict_size = 8000
|
||||
source_dict_size = dict_size
|
||||
target_dict_size = dict_size
|
||||
word_vector_dim = 128
|
||||
encoder_dim = 128
|
||||
decoder_dim = 128
|
||||
beam_size = 5
|
||||
max_length = 120
|
||||
|
||||
# encoder
|
||||
src_word_id = pd.data(
|
||||
name='source_language_word',
|
||||
type=pd.data.integer_value_sequence(source_dict_dim))
|
||||
src_embedding = pd.embedding(size=source_dict_size, size=word_vector_dim)
|
||||
|
||||
src_word_vec = pd.lookup(src_embedding, src_word_id)
|
||||
|
||||
encoder_out_seq = pd.gru(input=src_word_vec, size=encoder_dim)
|
||||
|
||||
encoder_ctx = pd.last_seq(encoder_out_seq)
|
||||
# encoder_ctx_proj is the learned semantic vector
|
||||
encoder_ctx_proj = pd.fc(
|
||||
encoder_ctx, size=decoder_dim, act=pd.activation.Tanh(), bias=None)
|
||||
```
|
||||
|
||||
**Decoder**
|
||||
|
||||
```python
|
||||
def generate():
|
||||
decoder = pd.while_loop()
|
||||
with decoder.step():
|
||||
decoder_mem = decoder.memory(init=encoder_ctx) # mark the memory
|
||||
generated_ids = decoder.memory() # TODO init to batch_size <s>s
|
||||
generated_scores = decoder.memory() # TODO init to batch_size 1s or 0s
|
||||
|
||||
target_word = pd.lookup(trg_embedding, gendrated_ids)
|
||||
# expand encoder_ctx's batch to fit target_word's lod
|
||||
# for example
|
||||
# decoder_mem.lod is
|
||||
# [[0 1 3],
|
||||
# [0 1 3 6]]
|
||||
# its tensor content is [a1 a2 a3 a4 a5]
|
||||
# which means there are 2 sentences to translate
|
||||
# - the first sentence has 1 translation prefixes, the offsets are [0, 1)
|
||||
# - the second sentence has 2 translation prefixes, the offsets are [1, 3) and [3, 6)
|
||||
# the target_word.lod is
|
||||
# [[0, 1, 6]
|
||||
# [0, 2, 4, 7, 9 12]]
|
||||
# which means 2 sentences to translate, each has 1 and 5 prefixes
|
||||
# the first prefix has 2 candidates
|
||||
# the following has 2, 3, 2, 3 candidates
|
||||
# the encoder_ctx_expanded's content will be
|
||||
# [a1 a1 a2 a2 a3 a3 a3 a4 a4 a5 a5 a5]
|
||||
encoder_ctx_expanded = pd.lod_expand(encoder_ctx, target_word)
|
||||
decoder_input = pd.fc(
|
||||
act=pd.activation.Linear(),
|
||||
input=[target_word, encoder_ctx],
|
||||
size=3 * decoder_dim)
|
||||
gru_out, cur_mem = pd.gru_step(
|
||||
decoder_input, mem=decoder_mem, size=decoder_dim)
|
||||
scores = pd.fc(
|
||||
gru_out,
|
||||
size=trg_dic_size,
|
||||
bias=None,
|
||||
act=pd.activation.Softmax())
|
||||
# K is an config
|
||||
topk_scores, topk_ids = pd.top_k(scores, K)
|
||||
topk_generated_scores = pd.add_scalar(topk_scores, generated_scores)
|
||||
|
||||
selected_ids, selected_generation_scores = decoder.beam_search(
|
||||
topk_ids, topk_generated_scores)
|
||||
|
||||
# update the states
|
||||
decoder_mem.update(cur_mem) # tells how to update state
|
||||
generated_ids.update(selected_ids)
|
||||
generated_scores.update(selected_generation_scores)
|
||||
|
||||
decoder.output(selected_ids)
|
||||
decoder.output(selected_generation_scores)
|
||||
|
||||
translation_ids, translation_scores = decoder()
|
||||
```
|
||||
The `decoder.beam_search` is a operator that given the candidates and the scores of translations including the candidates,
|
||||
return the result of the beam search algorithm.
|
||||
|
||||
In this way, users can customize anything on the inputs or outputs of beam search, for example, two ways to prune some translation prefixes
|
||||
|
||||
1. meke the correspondind elements in `topk_generated_scores` zero or some small values, beam_search will discard this candidate.
|
||||
2. remove some specific candidate in `selected_ids`
|
||||
3. get the final `translation_ids`, remove the translation sequence in it.
|
||||
|
||||
The implementation of sequence decoder can reuse the C++ class [RNNAlgorithm](https://github.com/Superjom/Paddle/blob/68cac3c0f8451fe62a4cdf156747d6dc0ee000b3/paddle/operators/dynamic_recurrent_op.h#L30),
|
||||
so the python syntax is quite similar to a [RNN](https://github.com/Superjom/Paddle/blob/68cac3c0f8451fe62a4cdf156747d6dc0ee000b3/doc/design/block.md#blocks-with-for-and-rnnop).
|
||||
|
||||
Both of them are two-level `LoDTensors`
|
||||
|
||||
- the first level represents `batch_size` of (source) sentences;
|
||||
- the second level represents the candidate ID sets for translation prefix.
|
||||
|
||||
for example, 3 source sentences to translate, and has 2, 3, 1 candidates.
|
||||
|
||||
Unlike an RNN, in sequence decoder, the previous state and the current state have different LoD and shape,
|
||||
a `lod_expand` operator is used to expand the LoD of the previous state to fit the current state.
|
||||
|
||||
For example, the previous state
|
||||
|
||||
* LoD is `[0, 1, 3][0, 2, 5, 6]`
|
||||
* content of tensor is `a1 a2 b1 b2 b3 c1`
|
||||
|
||||
the current state stored in `encoder_ctx_expanded`
|
||||
|
||||
* LoD is `[0, 2, 7][0 3 5 8 9 11 11]`
|
||||
* the content is
|
||||
- a1 a1 a1 (a1 has 3 candidates, so the state should be copied 3 times for each candidates)
|
||||
- a2 a2
|
||||
- b1 b1 b1
|
||||
- b2
|
||||
- b3 b3
|
||||
- None (c1 has 0 candidates, so c1 is dropped)
|
||||
|
||||
Benefit from the relative offset LoD, empty candidate set can be represented naturally.
|
||||
|
||||
the status in each time step can be stored in `TensorArray`, and `Pack`ed to a final LoDTensor, the corresponding syntax is
|
||||
|
||||
```python
|
||||
decoder.output(selected_ids)
|
||||
decoder.output(selected_generation_scores)
|
||||
```
|
||||
|
||||
the `selected_ids` is the candidate ids for the prefixes,
|
||||
it will be `Packed` by `TensorArray` to a two-level `LoDTensor`,
|
||||
the first level represents the source sequences,
|
||||
the second level represents generated sequences.
|
||||
|
||||
Pack the `selected_scores` will get a `LoDTensor` that stores scores of each candidate of translations.
|
||||
|
||||
Pack the `selected_generation_scores` will get a `LoDTensor`, and each tail is the probability of the translation.
|
||||
|
||||
## LoD and shape changes during decoding
|
||||
<p align="center">
|
||||
<img src="./images/LOD-and-shape-changes-during-decoding.jpg"/>
|
||||
</p>
|
||||
|
||||
According the image above, the only phrase to change LoD is beam search.
|
||||
|
||||
## Beam search design
|
||||
The beam search algorthm will be implemented as one method of the sequence decoder, it has 3 inputs
|
||||
|
||||
1. `topk_ids`, top K candidate ids for each prefix.
|
||||
2. `topk_scores`, the corresponding scores for `topk_ids`
|
||||
3. `generated_scores`, the score of the prefixes.
|
||||
|
||||
All of the are LoDTensors, so that the sequence affilication is clear.
|
||||
Beam search will keep a beam for each prefix and select a smaller candidate set for each prefix.
|
||||
|
||||
It will return three variables
|
||||
|
||||
1. `selected_ids`, the final candidate beam search function selected for the next step.
|
||||
2. `selected_scores`, the scores for the candidates.
|
||||
3. `generated_scores`, the updated scores for each prefixes (with the new candidates appended).
|
||||
|
||||
## Introducing the LoD-based `Pack` and `Unpack` methods in `TensorArray`
|
||||
The `selected_ids`, `selected_scores` and `generated_scores` are LoDTensors,
|
||||
and they exist in each time step,
|
||||
so it is natural to store them in arrays.
|
||||
|
||||
Currently, PaddlePaddle has a module called `TensorArray` which can store an array of tensors,
|
||||
the results of beam search are better to store in a `TensorArray`.
|
||||
|
||||
The `Pack` and `UnPack` in `TensorArray` are used to package tensors in the array to a `LoDTensor` or split the `LoDTensor` to an array of tensors.
|
||||
It needs some extensions to support pack or unpack an array of `LoDTensors`.
|
||||
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Reference in new issue