def step_gradient_descent(params, grad, alpha):
    """Single iteration of gradient descent.
    
    Args:
        params (ndarray[1, n]): parameters for current step
        grad (ndarray[1, n]):   gradient for current step
        alpha (float):          learning rate
    
    Returns:
        params (ndarray[1, n]): updated parameters
    """
    return params - alpha * grad