3 min readfrom Machine Learning

Obtaining Irregular Learning Curves with HyberBand Tuned ANN model for Price Prediction [P]

Our take

Achieving optimal performance with artificial neural networks (ANNs) often presents unexpected challenges. This case study explores an irregular learning curve observed after utilizing Hyperband for automated architecture tuning in a price prediction model, resulting in a perfect R² score—a potential indicator of overfitting. The investigation considers both code-related errors and inherent model behavior, seeking to understand the atypical loss representation. For further exploration of context within neural networks, consider "Context and average best linear mappings."
Obtaining Irregular Learning Curves with HyberBand Tuned ANN model for Price Prediction [P]

The machine learning community is perpetually grappling with the nuances of model training, and the recent Reddit post detailing an unusual learning curve following Hyperband tuning of an ANN for price prediction highlights a common, yet often perplexing, challenge. The user’s experience – a seemingly erratic validation/training loss curve coupled with a perfect R2 score – raises questions about code errors, model suitability, and the interpretation of these results. It’s a reminder that even with automated hyperparameter optimization tools like Hyperband, a deep understanding of the underlying mechanics and potential pitfalls remains crucial. This situation underscores the ongoing need for robust diagnostic techniques and a keen eye for anomalies in model behavior, something also touched upon in “Context and average best linear mappings [D],” which emphasizes the importance of considering the broader context within which neural networks operate, and how that context can influence results.

The perfect R2 score, while superficially impressive, is almost always a red flag, strongly suggesting overfitting. It’s less about the model learning the underlying relationship and more about memorizing the training data. Hyperband, designed to efficiently explore the hyperparameter space, can sometimes converge on a model that fits the training set *too* well, at the expense of generalization. The irregular learning curve further supports this suspicion. Ideally, both training and validation loss should decrease consistently, converging towards a stable point. The erratic behavior likely means the model is oscillating, struggling to find a stable solution that generalizes beyond the training data. The user’s question about whether this is a code issue or an inherent characteristic of the model is valid; while coding errors are possible, the described behavior aligns with overfitting scenarios. As addressed in “Public Library Find [D],” access to resources like O’Reilly books can provide valuable insights into debugging and addressing overfitting issues, demonstrating the importance of foundational knowledge alongside sophisticated tools.

Addressing this requires a multifaceted approach. First, a thorough review of the code, particularly the Hyperband configuration and the model architecture, is warranted. Double-checking the data preprocessing pipeline and ensuring proper validation set splitting is also essential. Techniques to mitigate overfitting, such as regularization (L1 or L2), dropout layers, or early stopping (already implemented in the code but potentially requiring adjustments to the patience parameter) should be explored. Furthermore, it's important to consider the complexity of the model relative to the amount of training data. A simpler model with fewer parameters might be more appropriate if the dataset is relatively small. Experimentation with different activation functions and layer configurations, possibly guided by the insights from “Where to publish a construction BIM Benchmark? [D],” which speaks to the iterative nature of model building, is also beneficial. Ultimately, the goal is to find a balance between model complexity and generalization ability.

The user’s dilemma highlights a critical point: automated tools, while powerful, are not a substitute for understanding the fundamentals of machine learning. Hyperband simplifies the hyperparameter optimization process, but it doesn’t eliminate the need for careful monitoring, analysis, and interpretation of results. The unusual learning curve is a signal, not a failure. It's an opportunity to deepen understanding and refine the modeling approach. The question now becomes: how can we better equip practitioners to not just *use* these automated tools, but to *understand* the stories they tell – even when those stories are unconventional, and what new diagnostic techniques will emerge to help us interpret these increasingly complex model training behaviors?

Obtaining Irregular Learning Curves with HyberBand Tuned ANN model for Price Prediction [P]

I have used Hyperband automatic tuning for an ANN model to predict price. After running HyberBand automatic tuning to get the 'best' architecture, I am obtaining a strange Val/Training loss learning curve. I cannot figure out if this is due to an error within the code or just a case of me not understanding the graph and not be able to interpret why the graph is showing as it is. I am also obtaining an R2 score of 1.00 which may suggest overfitting. I've not come across a learning curve (only shown the most basic learning curves at Uni) such as this as of yet so any advice would be greatly appreciated!

Here is the code for the actual tuning, in case it is due to a coding error but I am not sure that is the case.

def model_builder(hp):

model = tf.keras.Sequential()

model.add(tf.keras.layers.Flatten(input_dim = (train_final.shape[1])))

#creating activation choices - choosing betweeen relu and tanh

hp_activation = hp.Choice('activation', values = ['relu', 'tanh'])

#creating node choices - maxing unit amounts to 500

hp_layer_1 = hp.Int('layer_1', min_value=1, max_value=500, step=100)

hp_layer_2 = hp.Int('layer_2', min_value=1, max_value=500, step=100)

#creating learning rate choice - choice between 0.01, 0.001, 0.0001

hp_learning_rate = hp.Choice('learning_rate', values = [1e-2, 1e-3, 1e-4])

#specifies first layer after the flatten layer

model.add(tf.keras.layers.Dense(units = hp_layer_1, activation = hp_activation))

#creating the second layer

model.add(tf.keras.layers.Dense(units = hp_layer_2, activation = hp_activation))

model.add(tf.keras.layers.Dense(1, activation='linear'))

model.compile(optimizer=tf.keras.optimizers.Adam(learning_rate = hp_learning_rate),

loss tf.keras.losses.MeanSquaredError(), metrics = ['mean_absolute_error'])

return model

import keras_tuner as kt

#creating the tuner

tuner = kt.Hyperband(model_builder,

objective = 'val_loss',

max_epochs = 50,

factor = 3,

directory = 'dir',

project_name = 'x',

overwrite = True) # makes tuner rewrite over old tuning experiments

#adding early stopping - stops each model from running too long

stop_early = tf.keras.callbacks.EarlyStopping(monitor = 'val_loss', patience = 5)

tuner.search(train_final, y_train, epochs = 50, validation_split = 0.2, callbacks = [stop_early])

best_hp = tuner.get_best_hyperparameters(num_trials=1)[0]

best_hp.values

#obtaining the best model

best_model = tuner.get_best_models(num_models = 1)[0]

history = best_model.fit(train_final, y_train, epochs = 50, validation_split = 0.2, callbacks=[stop_early])

tuned_df = pd.DataFrame(history.history)

#running epoch loss visual def

epoch_loss_visual(tuned_df, model_name = 'Automatic Tuning Model')

Could it be an issue with the code itself causing the issue or is it simply the way the model is? If it's a case of it's just a bad model, I do not need to improve at the moment, but do need to understand the results, especially that of the learning curve representation.

submitted by /u/Grouchy-Archer3034
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