fit method

void fit(List<List<double>> X)

Implementation

void fit(List<List<double>> X) {
  final n = X.length;
  if (n == 0) throw ArgumentError('Empty dataset');
  final m = X[0].length;
  final rnd = Random(0);

  w1 = List.generate(
    m,
    (_) => List.generate(hidden, (_) => rnd.nextDouble() * 0.01),
  );
  w2 = List.generate(
    hidden,
    (_) => List.generate(m, (_) => rnd.nextDouble() * 0.01),
  );
  b1 = List<double>.filled(hidden, 0.0);
  b2 = List<double>.filled(m, 0.0);

  for (var epoch = 0; epoch < epochs; epoch++) {
    // Forward pass
    final Z = _matMul(X, w1!);
    for (var i = 0; i < Z.length; i++) {
      for (var j = 0; j < Z[0].length; j++) {
        Z[i][j] += b1![j];
      }
    }
    // ReLU
    for (var i = 0; i < Z.length; i++) {
      for (var j = 0; j < Z[0].length; j++) {
        Z[i][j] = max(0.0, Z[i][j]);
      }
    }
    var recon = _matMul(Z, w2!);
    for (var i = 0; i < recon.length; i++) {
      for (var j = 0; j < recon[0].length; j++) {
        recon[i][j] += b2![j];
      }
    }
    // compute simple gradients (MSE) and update (very small step implementation)
    final gradOut = List.generate(n, (_) => List<double>.filled(m, 0.0));
    for (var i = 0; i < n; i++) {
      for (var j = 0; j < m; j++) {
        gradOut[i][j] = recon[i][j] - X[i][j];
      }
    }
    final dW2 = List.generate(hidden, (_) => List<double>.filled(m, 0.0));
    for (var i = 0; i < hidden; i++) {
      for (var j = 0; j < m; j++) {
        for (var t = 0; t < n; t++) {
          dW2[i][j] += Z[t][i] * gradOut[t][j];
        }
      }
    }
    final dW1 = List.generate(m, (_) => List<double>.filled(hidden, 0.0));
    for (var i = 0; i < m; i++) {
      for (var j = 0; j < hidden; j++) {
        for (var t = 0; t < n; t++) {
          dW1[i][j] += X[t][i] * gradOut[t][j] * (Z[t][j] > 0 ? 1.0 : 0.0);
        }
      }
    }
    // updates
    for (var i = 0; i < m; i++) {
      for (var j = 0; j < hidden; j++) {
        w1![i][j] -= lr * dW1[i][j];
      }
    }
    for (var i = 0; i < hidden; i++) {
      for (var j = 0; j < m; j++) {
        w2![i][j] -= lr * dW2[i][j];
      }
    }
    for (var j = 0; j < hidden; j++) {
      for (var i = 0; i < n; i++) {
        b1![j] -= lr * gradOut[i][j];
      }
    }
    for (var j = 0; j < m; j++) {
      for (var i = 0; i < n; i++) {
        b2![j] -= lr * gradOut[i][j];
      }
    }
  }
}