
Number Theory Number Theory Math Forum 
 LinkBack  Thread Tools  Display Modes 
November 26th, 2017, 09:57 PM  #1 
Newbie Joined: Nov 2017 From: India Posts: 3 Thanks: 0  Properties of noninteger combinations
A linear combination, ax+by+...=z, where a,b,...,z∈Z and x,y,...∈Z. It is bound to yield an integer by the closure property of integers under the addition operation. This fact is used in computing g.c.d. among others. I want to know about properties of noninteger combination, i.e. given a,b,...∈Z; but the multipliers x,y,.. not all ∈ Z. I hope that they must be enjoying similar properties, as they are comprised of rationals, and the rationals are closed under addition too. If so, then how the property (of closure of rationals under addition) can be used where the linear combinations do not hold. A familiar case is in g.c.d. computation, where the invariant property (g.c.d. is same at each step) is a product of two linear equations being followed at each step that lead to common divisors of two pairs: (i) remainder (r), divisor(a), & (ii) dividend (d), and divisor(a). The Euclid algorithm reduces the quantities of dividend(d), divisor(a) at each step, while keeping the invariant property being followed. In (i) & (ii), d & r are the linear combinations respectively. Quotient (q) and divisor (a) are not linear combinations as when taken on l.h.s. lead to r.h.s. side expressions of d−r/a & d−r/q respectively. Definitely the expression given by dr/q or dr/a is a rational expression, and rationals are closed w.r.t. to the addition operation. I want to know, as curiosity, what properties are enjoyed by the two quantities that are not linear combination of integers. 
November 28th, 2017, 05:09 AM  #2 
Math Team Joined: Jan 2015 From: Alabama Posts: 3,261 Thanks: 896 
I am not clear what you are asking. You start by saying "multipliers x,y,.. not all ∈ Z". From just that they could be irrational. But then you say "as they are comprised of rationals". That sounds like you are thinking that is they are not integers, they must be rational, which is, of course, not true. Do you mean that you are requiring these numbers to be rational? If so then for any sum, ax+by+...=z, you can multiply by the least common denominator of the rational number to get back to the integer case. Any thing that is true of such a sum with integer multipliers is true with rational number multipliers.

November 28th, 2017, 07:26 AM  #3 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,600 Thanks: 2587 Math Focus: Mainly analysis and algebra 
The GCD is not a function with an equivalent in the rationals either.

November 29th, 2017, 08:22 PM  #4  
Newbie Joined: Nov 2017 From: India Posts: 3 Thanks: 0  Quote:
Last edited by ajiten; November 29th, 2017 at 08:27 PM.  
November 29th, 2017, 08:30 PM  #5 
Newbie Joined: Nov 2017 From: India Posts: 3 Thanks: 0  My question was specifically in reference to the fraction (d  r)/q or (d r)/a being a rational and not an integer. I meant that the properties of linear combinations are not enjoyed by a rational. So, a and q can not be expressed as a linear combination of the other terms.


Tags 
combinations, noninteger, noninteger, properties 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Some log properties  tiba  Algebra  8  June 27th, 2012 04:23 AM 
Properties of Integer Arithmetic  toughcookie723  Number Theory  2  December 4th, 2011 10:15 PM 
Complex Combinations Within Combinations Problem?  bugrocket  Advanced Statistics  2  January 23rd, 2011 05:02 PM 
Combinations within combinations possibilities?  aimpro2000  Advanced Statistics  2  September 20th, 2010 03:12 PM 
Proof of a subset of integer numbers and linear combinations  uberbandgeek6  Number Theory  1  February 4th, 2010 07:27 AM 