The exact tree method is the default and most precise way for XGBoost to build trees.

It enumerates all possible splits to find the optimal one, leading to better performance, especially on small datasets, but at the cost of slower training times compared to approximate methods.

Here’s an example demonstrating how to configure an XGBoost model with the exact tree method for a regression task using a synthetic dataset:

```
from sklearn.datasets import make_regression
from sklearn.model_selection import train_test_split
from xgboost import XGBRegressor
from sklearn.metrics import mean_squared_error
# Generate a synthetic regression dataset
X, y = make_regression(n_samples=1000, n_features=10, noise=0.1, random_state=42)
# Split the data into training and testing sets
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)
# Initialize an XGBRegressor with exact tree method
model = XGBRegressor(tree_method='exact', max_depth=5, learning_rate=0.1, n_estimators=100)
# Train the model
model.fit(X_train, y_train)
# Make predictions on the test set
predictions = model.predict(X_test)
# Evaluate the model
mse = mean_squared_error(y_test, predictions)
print(f"Mean Squared Error: {mse:.4f}")
```

In this example, we first generate a synthetic regression dataset using `make_regression()`

from scikit-learn. We then split the data into training and testing sets.

Next, we initialize an `XGBRegressor`

with `tree_method='exact'`

and set several other hyperparameters:

`max_depth`

: The maximum depth of each tree. Default is 6.`learning_rate`

: The step size shrinkage used in update to prevents overfitting. Default is 0.3.`n_estimators`

: The number of trees to fit. Default is 100.

We then train the model using the `fit()`

method, make predictions on the test set using `predict()`

, and evaluate the model’s performance using `mean_squared_error()`

.

Although using the exact tree method can be computationally expensive, it can lead to improved performance, particularly on smaller datasets or when high precision is required. However, for large datasets or when training time is a concern, approximate methods like `tree_method='approx'`

or `tree_method='hist'`

may be preferred.

As with any model, it’s essential to tune the hyperparameters to find the optimal balance between model complexity and generalization. Experiment with different values for `max_depth`

, `learning_rate`

, and `n_estimators`

to find the best combination for your specific problem.