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Title: Capacity of Deep Neural Networks under Parameter Quantization

Paper content:
Most deep neural networks (DNNs) require complex models to achieve high performance.
Parameter quantization is widely used for reducing the implementation complexities.
Previous studies on quantization were mostly based on extensive simulation using training data.
We choose a different approach and attempt to measure the per-parameter capacity of DNN models and interpret the results to obtain insights on optimum quantization of parameters.
This research uses artificially generated data and generic forms of fully connected DNNs, convolutional neural networks, and recurrent neural networks.
We conduct memorization and classification tests to study the effects of the number and precision of the parameters on the performance.
The model and the per-parameter capacities are assessed by measuring the mutual information between the input and the classified output.
We also extend the memorization capacity measurement results to image classification and language modeling tasks.
To get insight for parameter quantization when performing real tasks, the training and test performances are compared.
Deep neural networks (DNNs) have achieved impressive performance on various machine learning tasks.
Several DNN architectures are known, and the most famous ones are fully connected DNNs (FCDNNs), convolutional neural networks (CNNs), and recurrent neural networks (RNNs).It
is known that neural networks do not need full floating-point precision for inference BID10 BID16 BID23 . A
32-bit floating-point parameter can be reduced to 8-bit, 4-bit, 2-bit, or 1-bit, but this can incur performance degradation. Therefore
, precision should be optimized, which is primarily conducted by extensive computer simulations using training data. This not
only takes much time for optimization but also can incorrectly predict the performance in real environments when the characteristics of input data are different from the training data.In this study, we attempt to measure the capacity of DNNs, including FCDNN, CNN, and RNN, using a memorization and classification task that applies random binary input data. The per-parameter
capacities of various models are estimated by measuring the mutual information between the input data and the classification output. Then, the fixed-point
performances of the models are measured to determine the relation between the quantization sensitivity and the per-parameter capacity. The memorization capacity
analysis results are extended to real models for performing image classification and language modeling, by which the parameter quantization sensitivity is compared between memorization and generalization tasks.The contributions of this paper are as follows.• We experimentally measure
the memorization capacity of DNNs and estimate the perparameter capacity. The capacity per parameter
is between 2.3 bits to 3.7 bits, according to the network structure, which is FCDNN, CNN, or RNN. The value is fairly independent
of the model size.• We show that the performance of
the quantized networks is closely related to the capacity per parameter, and FCDNNs show the most resilient quantization performance while RNNs suffer most from parameter quantization. The network size hardly effects the
quantization performance when DNN models are trained to use full capacity.• We explain that severe quantization
, such as binary or ternary weights, can be employed without much performance degradation when the networks are in the over-parameter region.• We suggest the sufficient number of
bits for representing weights of neural networks, which are approximately 6 bits, 8 bits, and 10 bits for FCDNNs, CNNs, and RNNs, respectively. This estimate of the number of bits for
implementing neural networks is very important considering that many accelerators are designed without any specific training data or applications.• The study with real-models shows that
neural networks are more resilient to quantization when performing generalization tasks than conducting memorization. Thus, the optimum bits obtained with the
memorization tasks are conservative and safe estimate when solving real problems.The paper is organized as follows. In Section 2, previous works on neural network
capacity and fixedpoint optimization are briefly presented. Section 3 explains the capacity measurement methods
for DNN models. Section 4 presents parameter capacity measurement results
for FCDNNs, CNNs, and RNNs. The quantization performances measured on DNNs are presented
in Section 5. Concluding remarks follow in Section 6.

assistant: text: We suggest the sufficient number of bits for representing weights of DNNs and the optimum bits are conservative when solving real problems.