数学

def fibonacci(n):
    if n <= 1:
        return n
    else:
        return fibonacci(n-1) + fibonacci(n-2)

def filter_even_numbers(lst):
    return [num for num in lst if num % 2 == 0]

def find_median(dataset):
    sorted_list = sorted(dataset)
    length = len(sorted_list)
    if length % 2 == 0:
        return (sorted_list[length // 2 - 1] + sorted_list[length // 2]) / 2
    else:
        return sorted_list[length // 2]

def calculate_variance(data):
    mean = sum(data) / len(data)
    return sum((x - mean) ** 2 for x in data) / len(data)

def calculate_std_deviation(data):
    variance = calculate_variance(data)
    return variance ** 0.5

def calculate_correlation(x, y):
    mean_x = sum(x) / len(x)
    mean_y = sum(y) / len(y)
    numerator = sum((xi - mean_x) * (yi - mean_y) for xi, yi in zip(x, y))
    denominator = (sum((xi - mean_x) ** 2 for xi in x) * sum((yi - mean_y) ** 2 for yi in y)) ** 0.5
    return numerator / denominator if denominator else 0