# I What's The Discrete Math Derivative Equivalent?

1. Apr 2, 2016

### iScience

$$ƒ = b^n$$
$$b,n,I ∈ ℤ$$

Condition: Upon choosing a base value $b$..

$$n | b^n ≤ I$$
(n is determined based off the value of $b$ to yield the highest ƒ without going over $I$)
$$1<b<L , L<<I$$
where $I$ is some large number, and $L$ is also sufficiently large such that we want to avoid going through each base integer via trial and error....

How might I determine the base value that yields a value $ƒ$ that is closest to $I$?

2. Apr 4, 2016

### andrewkirk

I'm not sure exactly what you are asking.
Are you asking how to, given $L,I\in\mathbb{Z}$ with $0<<L<<I$, find the combination $b,n\in\mathbb{Z}$ that maximizes $b^n$ subject to the constraints
1. $1<b<L$; and
2. $b^n<I$

If so then you could set $Hi=\lfloor\log_2 I\rfloor$ and $Lo=\lceil \log_L I\rceil$, then find
$$b^n=max_{Lo\leq m\leq Hi}\bigg( \lfloor I^\tfrac{1}{m}\rfloor\bigg)^m$$

where $n$ is the value of $m$ that delivers that maximum.
That will give a much smaller search space than $1,...,L$.

Last edited: Apr 4, 2016