ChatGPT fibonacci answer

#produced by ChatGPT 4 February 2023 in response to the prompt "So in Python give a complete matrix exponentiation solution for finding the nth fibonacci number."

def fib(n):
    if n == 0:
        return 0
    if n == 1:
        return 1

    def mat_mult(A, B):
        C = [[0, 0], [0, 0]]
        for i in range(2):
            for j in range(2):
                C[i][j] = A[i][0] * B[0][j] + A[i][1] * B[1][j]
        return C

    def mat_pow(A, n):
        if n == 1:
            return A
        if n % 2 == 0:
            B = mat_pow(A, n//2)
            return mat_mult(B, B)
        else:
            return mat_mult(A, mat_pow(A, n-1))

    F = [[1, 1], [1, 0]]
    return mat_pow(F, n-1)[0][0]