Classification-Based Financial Markets Prediction Using Deep Neural Networks

Matthew Francis Dixon

Illinois Institute of Technology – Stuart School of Business, IIT

Diego Klabjan

Northwestern University

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Jin Hoon Bang

Northwestern University

May 18, 2016

Abstract:

Deep neural networks (DNNs) are powerful types of artificial neural networks (ANNs) that use several hidden layers. They have recently gained considerable attention in the speech transcription and image recognition community for their superior predictive properties including robustness to over fitting. However their application to algorithmic trading has not been previously researched, partly because of their computational complexity. This paper describes the application of DNNs to predicting financial market movement directions. In particular we describe the configuration and training approach and then demonstrate their application to back testing a simple trading strategy over 43 different Commodity and FX future mid-prices at 5-minute intervals. All results in this paper are generated using a C++ implementation on the Intel Xeon Phi co-processor which is 11.4x faster than the serial version and a Python strategy back testing environment both of which are available as open source code written by the authors.

Classification-Based Financial Markets Prediction Using Deep Neural Networks – Introduction

Many of the challenges facing methods of financial econometrics include non-stationarity, non-linearity or noisiness of the time series. While the application of artificial neural networks (ANNs) to time series methods are well documented (Faraway and Chatfield, 1998; Refenes, 1994; Trippi and DeSieno, 1992; Kaastra and Boyd, 1995) their proneness to over-fitting, convergence problems, and difficulty of implementation raised concerns. Moreover, their departure from the foundations of financial econometrics alienated the financial econometrics research community and finance practitioners.

However, algotrading firms employ computer scientists and mathematicians who are able to perceive ANNs as not merely black-boxes, but rather a non-parametric approach to modeling based on minimizing an entropy function. As such, there has been a recent resurgence in the method, in part facilitated by advances in modern computer architecture (Chen et al., 2013; Niaki and Hoseinzade, 2013; Vanstone and Hahn, 2010).

A deep neural network (DNN) is an artificial neural network with multiple hidden layers of units between the input and output layers. They have been popularized in the artificial intelligence community for their successful use in image classification (Krizhevsky et al., 2012) and speech recognition. The field is referred to as “Deep Learning”.

In this paper, we shall use DNNs to partially address some of the historical deficiencies of ANNs. Specifically, we model complex non-linear relationships between the independent variables and dependent variable and reduced tendency to overfit. In order to do this we shall exploit advances in low cost many-core accelerator platform to train and tune the parameters of our model.

For financial forecasting, especially in multivariate forecasting analysis, the feed-forward topology has gained much more attention and shall be the approach used here. Back-propagation and gradient descent have been the preferred method for training these structures due to the ease of implementation and their tendency to converge to better local optima in comparison with other trained models. However, these methods can be computationally expensive, especially when used to train deep neural networks.

There are many training parameters to be considered with a DNN, such as the size (number of layers and number of units per layer), the learning rate and initial weights. Sweeping through the parameter space for optimal parameters is not feasible due to the cost in time and computational resources. We shall use mini-batching (computing the gradient on several training examples at once rather than individual examples) as one common approach to speeding up computation. We go further by expressing the back-propagation algorithm in a form that is amenable to fast performance on an Intel Xeon Phi co-processor (Jeffers and Reinders, 2013). General purpose hardware optimized implementations of the back-propagation algorithm are described by Shekhar and Amin (1994), however our approach is tailored for the Intel Xeon Phi co-processor.

The main contribution of this paper is to describe the application of deep neural networks to financial time series data in order to classify financial market movement directions. Traditionally, researchers will iteratively experiment with a handful of signals to train a level based method, such as vector autoregression, for each instrument (see for example Kaastra and Boyd (1995); Refenes (1994); Trippi and DeSieno (1992)). More recently, however, Leung et al. (2000) provide evidence that classification based methods outperform level based methods in the prediction of the direction of stock movement and trading returns maximization.

Using 5 minute interval prices from June 1989 to March 2013, our approach departs from the literature by using state-of-the-art parallel computing architecture to simultaneously train a single model from a large number of signals across multiple instruments, rather than using one model for each instrument. By aggregating the data across multiple instruments and signals, we enable the model to capture a richer set of information describing the time-varying co-movements across signals for each instrument price movement. Our results show that our model is able to predict the direction of instrument movement to, on average, 42% accuracy with a standard deviation across instruments of 11%. In some cases, we are able to predict as high as 68%. We further show how backtesting accuracy translates into the P&L for a simple long-only trading strategy and demonstrate sample mean Annualized Sharpe Ratios as high as 3.29 with a standard deviation of 1.12.

So in summary, our approach differs from other financial studies described in the literature in two distinct ways:

ANNs are applied to historical prices on an individual symbol and here 43 commodities and FX futures traded on the CME have been combined. Furthermore time series of lags, moving averages and moving correlations have been generated to capture memory and co-movements between symbols. Thus we have generated a richer dataset for the deep neural networks to explore complex patterns. ANNs are applied as a regression, whereas here the output is one of {-1,0,1} 1g representing a negative, at or positive price movement respectively. The threshold for determining the zero state is set to 1×106^-3 (this is chosen to balance the class labels). The caveat is that restriction to a discrete set of output states may not replace a classical financial econometric technique, but it may be applicable for simple trading strategies which rely on the sign, and not the magnitude, of the forecasted price.

In the following section we introduce the back-propagation learning algorithm and use mini-batching to express the most compute intensive equations in matrix form. Once expressed in matrix form, hardware optimized numerical linear algebra routines are used to achieve an efficient mapping of the algorithm on to the Intel Xeon Phi co-processor. Section 3 describes the preparation of the data used to train the DNN. Section 4 describes the implementation of the deep neural networks. Section 5 then presents results measuring the performance of a DNN. Finally in Section 6, we demonstrate the application of DNNs to backtesting using a walk forward methodology, and provide performance results for a simple buy-hold-sell strategy.

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