bi_funct_search

bi_funct_search.py

def bi_funct_search(f, x, low=0, high=None):
    """a text book binary search against a function
        f is a strictly increasing function
        x is a number in (low, high) and the domain of f
        low is lower bound
        high is upperbound (usually should not be omitted)
        returns z such that f(z) = x or None if not found"""
    if high is None:
        high = x ** 2
    while low < high:
        mid = (low + high) // 2
        midval = f(mid)
        if midval < x:
            low = mid + 1
        elif midval > x:
            high = mid
        else:
            return mid
    return None  # to show x was not found