Merge pull request #33 from jideoyelayo1/MLR

Author: jideoyelayo1

ml_library_include/ml/regression/MultiLinearRegression.hpp

@@ -8,11 +8,11 @@
 
 /**
  * @file MultilinearRegression.hpp
- * @brief A simple implementation of Multi Linear Regression.
+ * @brief A simple implementation of Multilinear Regression with improvements.
  */
 
 /**
- * @class Multilinear Regression
+ * @class MultilinearRegression
  * @brief A class that implements Multilinear Regression for predicting values
  * based on multiple features.
  */
@@ -23,9 +23,10 @@ class MultilinearRegression {
      *
      * @param learningRate The rate at which the model learns (default 0.01).
      * @param iterations The number of iterations for the gradient descent (default 1000).
+     * @param regularizationParameter The regularization parameter lambda (default 0.0, no regularization).
      */
-    MultilinearRegression(double learningRate = 0.01, int iterations = 1000)
-        : learningRate(learningRate), iterations(iterations) {}
+    MultilinearRegression(double learningRate = 0.01, int iterations = 1000, double regularizationParameter = 0.0)
+        : learningRate_(learningRate), iterations_(iterations), lambda_(regularizationParameter) {}
 
     /**
      * @brief Trains the Multilinear Regression model on the provided data.
@@ -39,10 +40,23 @@ class MultilinearRegression {
             throw std::invalid_argument("Features and target data sizes do not match.");
         }
 
-        int numFeatures = features[0].size();
-        weights.resize(numFeatures, 0.0);  // Initialize weights
+        size_t numSamples = features.size();
+        size_t numFeatures = features[0].size();
 
-        for (int i = 0; i < iterations; ++i) {
+        // Validate that all feature vectors have the same size
+        for (const auto& feature : features) {
+            if (feature.size() != numFeatures) {
+                throw std::invalid_argument("All feature vectors must have the same number of elements.");
+            }
+        }
+
+        // Initialize weights and bias if they haven't been initialized yet
+        if (weights_.empty()) {
+            weights_.resize(numFeatures, 0.0);
+            bias_ = 0.0;
+        }
+
+        for (int iter = 0; iter < iterations_; ++iter) {
             gradientDescentStep(features, target);
         }
     }
@@ -54,13 +68,38 @@ class MultilinearRegression {
      * @return The predicted value.
      */
     double predict(const std::vector<double>& features) const {
-        return std::inner_product(weights.begin(), weights.end(), features.begin(), 0.0);
+        if (features.size() != weights_.size()) {
+            throw std::invalid_argument("Feature vector size does not match the number of weights.");
+        }
+        double result = std::inner_product(weights_.begin(), weights_.end(), features.begin(), 0.0);
+        result += bias_;
+        return result;
+    }
+
+    /**
+     * @brief Gets the current weights of the model.
+     *
+     * @return A vector containing the weights.
+     */
+    std::vector<double> getWeights() const {
+        return weights_;
+    }
+
+    /**
+     * @brief Gets the current bias of the model.
+     *
+     * @return The bias term.
+     */
+    double getBias() const {
+        return bias_;
     }
 
 private:
-    double learningRate;            ///< The learning rate for gradient descent.
-    int iterations;                 ///< The number of iterations for training.
-    std::vector<double> weights;    ///< The weights for the model.
+    double learningRate_;            ///< The learning rate for gradient descent.
+    int iterations_;                 ///< The number of iterations for training.
+    double lambda_;                  ///< Regularization parameter (lambda).
+    std::vector<double> weights_;    ///< The weights for the model.
+    double bias_ = 0.0;              ///< Bias term.
 
     /**
      * @brief Performs a single iteration of gradient descent to update the model weights.
@@ -69,20 +108,29 @@ class MultilinearRegression {
      * @param target A vector containing the target values.
      */
     void gradientDescentStep(const std::vector<std::vector<double>>& features, const std::vector<double>& target) {
-        std::vector<double> gradients(weights.size(), 0.0);
+        size_t numSamples = features.size();
+        size_t numFeatures = weights_.size();
+
+        std::vector<double> gradients(numFeatures, 0.0);
+        double biasGradient = 0.0;
 
-        for (size_t i = 0; i < features.size(); ++i) {
+        for (size_t i = 0; i < numSamples; ++i) {
             double prediction = predict(features[i]);
             double error = prediction - target[i];
 
-            for (size_t j = 0; j < weights.size(); ++j) {
-                gradients[j] += error * features[i][j];
+            for (size_t j = 0; j < numFeatures; ++j) {
+                gradients[j] += (error * features[i][j]) + (lambda_ * weights_[j]);
             }
+
+            biasGradient += error;
         }
 
-        for (size_t j = 0; j < weights.size(); ++j) {
-            weights[j] -= (learningRate / features.size()) * gradients[j];
+        // Update weights and bias
+        for (size_t j = 0; j < numFeatures; ++j) {
+            weights_[j] -= (learningRate_ / numSamples) * gradients[j];
         }
+
+        bias_ -= (learningRate_ / numSamples) * biasGradient;
     }
 };