verifySigmoid function

void verifySigmoid()

Implementation

void verifySigmoid() {
  final x = Tensor.fill([1, 1], 0.0);
  x.data = [0.0]; // sigmoid(0) = 0.5

  // We wrap it in sum to get a scalar loss for backward
  final loss = x.sigmoid().sum();
  loss.backward();

  final grads = x.grad;
  // d(sigmoid(x))/dx = sig(x) * (1 - sig(x))
  // At x=0: 0.5 * (1 - 0.5) = 0.25
  bool ok = closeEnough(grads[0], 0.25);
  print(
    "SIGMOID: ${ok ? '✅ PASS' : '❌ FAIL (Expected 0.25, got ${grads[0]})'}",
  );
}