Seminar Details
2021-11-23 (14h) : Implementing spintronic based neuromorphic computing hardware under the reservoir computing approach
At Euler building (room a.002)
Organized by Mathematical Engineering
Speaker :
Flavio Abreu Araujo (UCLouvain)
Abstract :
The brain displays many signatures of non-linear dynamical behavior, including synchronization and complex transient behavior. These observations have inspired a whole class of neuromorphic concepts based on complex networks of interconnected non-linear nodes. Such non-linearity has been identified as one of the main ingredients to achieve excellent performance in cognitive tasks such as spoken digit recognition. In this work, we have quantified in detail the contribution of the acoustic filtering and the neural network, respectively, for spoken digit recognition task using three different frequency decomposition methods: Cochlear, MFCC and Spectrogram. In a first step, we have demonstrated that Cochlear and MFCC are powerful stand-alone features extractors, and they can achieve for themselves very high recognition level: up to 95.8% and 77.2% for cochlear and MFCC, respectively. We have found that such high recognition level is mainly due to the non-linear character of these frequency decomposition methods. First, we have investigated the non- linear dependence of the Spectrogram showing a huge increase of recognition rate from 10% (linear) to 85.6%. In a second step, we have evaluated the gain of the recognition rate provided by the neural network. For simplicity, we have modeled a neural network based on the non- linear dynamics of oscillators in the framework of the reservoir computing approach. The reservoir is generally composed by a large number of fixed and random interconnected non- linear oscillators which generates very complex non-linear dynamics. The key insight behind reservoir computing is that only the external connections (between the reservoir and the output layer) should be trained to obtain the desirable target. Reservoir computing has been identified to be very suitable for different hardware implementations: optical, photonic and spintronic devices. We have found that the contribution of the neural network is dominant for the linear Spectrogram filter but not in the other two cases, i.e., cochlear and MFCC. Finally, we have carried out experiments using non-linear and tunable spin-torque nano-oscillators exhibiting an excellent agreement with our simulations.