IAOA-LSTM: a hybrid model for stock portfolio optimization

This study introduces a novel hybrid model, the Improved Arithmetic Optimization Algorithm Long Short-Term Memory (IAOA-LSTM), tailored for portfolio selection in the biotechnology and oil & gas sectors.
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The journey that led to this paper began in late 2022, during a series of discussions between our team members across Nigeria and Hong Kong. We were observing something fascinating while deep learning had revolutionized many domains, its application to portfolio optimization in highly volatile sectors remained surprisingly conservative. Most investors in biotechnology and oil and gas were still relying on traditional financial models that struggled to capture the nonlinear, temporal dependencies inherent in these markets. We asked ourselves a simple question: could we build something better?

The core challenge we faced was fundamental. Long Short-Term Memory networks excelled at learning sequential patterns in time-series data, but their performance hinged critically on hyperparameter selection. Getting this wrong meant poor forecasts, and poor forecasts meant poor investment decisions. Meanwhile, metaheuristic optimization algorithms like the Arithmetic Optimization Algorithm offered powerful global search capabilities but were not designed specifically for deep learning architectures. The idea was elegantly simple: what if we could make them work together synergistically? Temitope, who was working on deep learning applications at The Hong Kong Polytechnic University, had been experimenting with various optimization techniques for financial forecasting. David and Yahya, at Federal University Kashere, brought deep expertise in mathematical modeling and statistical validation. Temidayo, at the Federal University of Health Sciences, contributed crucial insights on algorithmic efficiency and real-world applicability.

I distinctly recall the afternoon when everything clicked. We were reviewing the standard AOA equations when Temidayo observed that the Math Optimizer Accelerated function seemed to bias the search toward one side of the solution space and asked what if we recentered it. That simple observation led to our improved formulation which recentered the search around the midpoint of the solution space and enabled more efficient exploration during early iterations. Similarly, we introduced an exponential scaling function for the Math Optimizer Probability, creating a smoother transition between exploration and exploitation phases. When we first ran the integrated IAOA-LSTM model and saw the results, there was genuine excitement in our virtual meeting room. The error metrics were substantially lower than anything we had achieved with standard LSTM, GRU, or even other optimization-enhanced variants.

Working with financial data spanning a decade from 2012 to 2022 presented its own set of challenges. We had deliberately chosen two of the most volatile sectors, biotechnology and oil and gas, to rigorously test our model's robustness. Biotechnology stocks like SRPT and ALNY exhibited extraordinary volatility with kurtosis values exceeding 324 and 50 respectively, while oil and gas stocks like XOM and CVX offered more stable but still dynamic patterns. There were moments of frustration. Early versions of our model would occasionally converge on local optima, selecting stocks that looked excellent in training but performed poorly in validation. Each failure taught us something valuable about the delicate balance between exploration and exploitation in the optimization process.

Perhaps the most gratifying moment came during statistical validation. When we ran the paired t-tests comparing IAOA-LSTM against benchmark models, the p-values consistently returned 0.0000. This was not just incremental improvement; it was statistically unambiguous evidence that our hybrid approach was genuinely superior. The reconstruction error-based ranking mechanism we developed for stock selection emerged as an unexpected highlight. By measuring the Euclidean distance between actual and predicted price changes, we created a principled method for identifying the most predictable stocks. This was not just about accuracy, it was about building investor confidence through transparency and reproducibility.

As we reflect on this work, we are acutely aware that the journey is far from over. The financial landscape continues to evolve, and with it, the challenges facing investors. Our current efforts are exploring three promising directions: integrating attention-based architectures like Transformers to capture even longer-range dependencies, incorporating multi-objective optimization criteria such as ESG compliance and transaction cost minimization, and developing real-time rebalancing capabilities for dynamic portfolio management. We are particularly excited about the potential of combining IAOA with emerging architectures like Helformer and Temporal Fusion Transformers. Early experiments suggest that attention mechanisms might complement our optimization approach in ways we are only beginning to understand.

What makes this work meaningful to us is not just the technical achievement, but its potential real-world impact. Portfolio optimization is not an abstract mathematical exercise, it affects real people's savings, retirements, and financial security. Knowing that our model could help investors in volatile sectors make more informed, data-driven decisions is profoundly motivating. We are grateful to our institutions, Federal University Kashere, Federal University of Health Sciences, and The Hong Kong Polytechnic University, for providing the environment and support that made this research possible. We are also indebted to the broader scientific community whose foundational work on LSTM networks, arithmetic optimization, and portfolio theory provided the building blocks for our contributions. This paper represents not an endpoint, but a milestone in an ongoing journey. We hope it inspires others to explore the rich intersection of deep learning and bio-inspired optimization, and we look forward to seeing where this path leads next.

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