Minimize |n-2^x*3^y| over the integer

  • Context: Undergrad 
  • Thread starter Thread starter a1call
  • Start date Start date
  • Tags Tags
    Integer
Click For Summary

Discussion Overview

The discussion revolves around the minimization of the expression |n - 2^x * 3^y| over integer values of x and y for a given integer n. Participants explore various approaches to find integer solutions that yield the smallest possible value of this expression.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents a numeric example for n = 6859, finding |6859 - 2^8 * 3^3| = 53, suggesting this might be a minimum.
  • Another participant challenges the initial claim, providing examples where smaller values can be achieved, such as |6 - 2^1 * 3^1| = 0.
  • A participant clarifies that n is a fixed integer, and the goal is to find integer values of x and y that minimize the expression, asserting that for n = 6859, the minimum is indeed 53 with x = 8 and y = 3.
  • Discussion includes the potential application of calculus techniques, such as Lagrange multipliers, although one participant expresses skepticism about their applicability to integer solutions.
  • Another participant notes that minimizing |2^x - 3^y| remains an open problem, suggesting that the problem at hand may not be simpler.
  • Logarithmic approaches are mentioned as a possible method to reduce the number of cases to test.

Areas of Agreement / Disagreement

Participants express differing views on the existence of a minimum value and the methods to find it. There is no consensus on a definitive solution or approach, and the discussion remains unresolved regarding the best techniques to apply.

Contextual Notes

Some limitations include the dependence on integer constraints, the challenge of applying calculus techniques to discrete variables, and the unresolved nature of the problem in the context of integer minimization.

a1call
Messages
90
Reaction score
5
Hi,
Is there a way to formulate the solution of minimization of:
abs(n-2^x*3^y)
Over integers x and y for any given integer n?
A numeric example that I found by trial and error is:
|6859-2^8*3^3|=53

Thanks in advance.
 
Mathematics news on Phys.org
a1call said:
Hi,
Is there a way to formulate the solution of minimization of:
abs(n-2^x*3^y)
Over integers x and y for any given integer n?
A numeric example that I found by trial and error is:
|6859-2^8*3^3|=53

Thanks in advance.
That's hardly a minimum value. If n = x = y = 1, the result is |-5| = 5
If n = 6 and x = y = 1, the result is 0, which would be minimum value for the parameter n = 6.

Have you studied calculus? In particular multivariate calculus? There are a couple of techniques that can be used to function the minimum or maximum of a function of two variables. There is also the technique of Lagrange multipliers.
 
Hi Mark44,
n is not meant to be a variable. It is a known integer value and the problem is to solve for integer variables x and y such that the result has smallest integer value. So for my numeric example n can only be 6859. x and y can be any integers. the minimization solution is x=8 and y= 3, because no other integer values of x and/or y will result in a number less than 53.
As far as I know calculus does offer solutions over the rational field but not over the integer field.
Would the Lagrange multipliers offer a general solution for this?
Thank you for the reply.
 
Last edited:
I don't expect there to be a known solution for this. I am just looking for expert-confirmation or authoritative-reference on the subject.
 
Positive integers? Otherwise there is no minimum.

Minimizing abs(2^x-3^y) apart from the case |8-9|=1 is still an open problem. Your problem doesn't look easier.

log(n)=x*log(2)+y*log(3) and some approximation techniques could help to reduce the number of cases to test.
 
Thank you for the reply mfb.
The log formula is very interesting.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
Replies
7
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K