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Quantum Support Vector Machine (QSVM)

QSVM formulates the feature selection step of SVM training as a QUBO problem, solved on the Dynex platform. This finds the optimal subset of features to maximize classification accuracy while minimizing model complexity.

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Installation

pip install dynex scikit-learn numpy

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Using the Dynex scikit-learn Plugin

The dynex_scikit_plugin provides a drop-in scikit-learn transformer: 
import numpy as np
from sklearn.datasets import load_breast_cancer
from sklearn.model_selection import train_test_split
from sklearn.svm import SVC
from sklearn.pipeline import Pipeline
from sklearn.preprocessing import StandardScaler

# Load the dynex scikit plugin
import sys
sys.path.append('examples/utils')
from dynex_scikit_plugin import DynexClassifier

from dynex import DynexConfig, ComputeBackend

# Load dataset
X, y = load_breast_cancer(return_X_y=True)
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)

# Build pipeline: scaler -> quantum feature selection -> SVM
config = DynexConfig(compute_backend=ComputeBackend.GPU)

pipeline = Pipeline([
    ('scaler', StandardScaler()),
    ('qsvm', DynexClassifier(config=config, num_reads=1000, annealing_time=200)),
])

pipeline.fit(X_train, y_train)
accuracy = pipeline.score(X_test, y_test)
print(f"Test accuracy: {accuracy:.4f}")

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Manual QSVM formulation

import dynex
import dimod
import numpy as np
from sklearn.datasets import make_classification
from dynex import DynexConfig, ComputeBackend

# Generate dataset
X, y = make_classification(n_samples=100, n_features=10, random_state=42)
y = 2 * y - 1  # Convert to {-1, +1}

# Build QUBO for feature selection
# Objective: select features that maximize margin while penalizing count
n_features = X.shape[1]
lambda_reg = 0.1  # Regularization weight

# Compute kernel matrix
K = X @ X.T

Q = {}
# Linear terms: negative contribution to SVM objective
for i in range(n_features):
    Q[(i, i)] = Q.get((i, i), 0) + lambda_reg

# Quadratic terms: correlations between features
for i in range(n_features):
    for j in range(i+1, n_features):
        correlation = np.abs(np.corrcoef(X[:, i], X[:, j])[0, 1])
        if correlation > 0.1:
            Q[(i, j)] = Q.get((i, j), 0) + correlation * lambda_reg

bqm = dimod.BinaryQuadraticModel.from_qubo(Q)
model = dynex.BQM(bqm)

config = DynexConfig(compute_backend=ComputeBackend.GPU)
sampler = dynex.DynexSampler(model, config=config)
sampleset = sampler.sample(num_reads=1000, annealing_time=200)

selected_features = [i for i, v in sampleset.first.sample.items() if v == 1]
print(f"Selected features: {selected_features}")

# Train classical SVM on selected features
from sklearn.svm import SVC
from sklearn.model_selection import cross_val_score

X_selected = X[:, selected_features]
svm = SVC(kernel='rbf')
scores = cross_val_score(svm, X_selected, y, cv=5)
print(f"Cross-validation accuracy: {scores.mean():.4f} ± {scores.std():.4f}")

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