Function as a Solution to Specific Conditions

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Discussion Overview

The discussion revolves around finding a function that satisfies the equation ##\frac{f\left(0\right)}{f\left(a\right)}f\left(x+a\right)=f\left(x\right)##, with a focus on the nature of potential solutions, particularly in the context of statistical mechanics and functional equations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant proposes that the function could be of the form ##f(x) = Ce^{\pm x}##.
  • Another participant expresses curiosity about how this solution was derived and questions whether exponential functions are the only solutions.
  • A participant explains their reasoning, noting that the relationship ##f(x) \propto f(x+a) / f(a)## suggests that an addition in the argument results in a multiplication of the function, leading them to recognize the exponential form.
  • There is mention of a constant function ##f(x) = \mathrm{const.}## as another possible solution.
  • One participant speculates that the topic may fall under Calculus, particularly in relation to limits and Taylor series.
  • Another participant suggests that the general solution could be expressed as ##f(x) = Ce^{d x}##, where C and d are arbitrary constants, and notes that this is a typical homework problem.
  • A later reply identifies the topic as "Functional equations," providing a link for further reference.

Areas of Agreement / Disagreement

Participants express varying viewpoints on the nature of solutions, with some proposing exponential functions while others suggest constants or more general forms. There is no consensus on whether exponential functions are the only solutions, and the discussion remains open-ended.

Contextual Notes

Participants do not fully resolve the question of whether other types of functions could satisfy the original equation, and there are references to different branches of mathematics without a definitive classification.

tade
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I'm trying to solve some statistical mechanics. This problem appeared.

##\frac{f\left(0\right)}{f\left(a\right)}f\left(x+a\right)=f\left(x\right)##

Any idea as to which function will satisfy this equation?
 
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##f(x) = Ce^{\pm x}##
 
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DrClaude said:
##f(x) = Ce^{\pm x}##
Nice. How did you work that out? Is an exponential function the only solution to this problem?
 
tade said:
Nice. How did you work that out?
From the observation that ##f(x) \propto f(x+a) / f(a)## requires that an addition in the argument becomes an (inverse) multiplication of the function, and I recognized the exponential. (I actually thought about log first, but then realized I had it backwards :smile:)

tade said:
Is an exponential function the only solution to this problem?
No idea. Apart from the answer I gave and ##f(x) = \mathrm{const.}##, I don't see any.
 
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DrClaude said:
From the observation that ##f(x) \propto f(x+a) / f(a)## requires that an addition in the argument becomes an (inverse) multiplication of the function, and I recognized the exponential. (I actually thought about log first, but then realized I had it backwards :smile:)
That's pretty neat. What branch of mathematics is that under?
 
tade said:
That's pretty neat. What branch of mathematics is that under?
I'm not a mathematician. It just comes from years of working with, and getting a feeling for, those kind of mathematical functions.
 
DrClaude said:
I'm not a mathematician. It just comes from years of working with, and getting a feeling for, those kind of mathematical functions.
No, I was just wondering what topic or branch this question falls under.
 
The general solution is ##f(x) = Ce^{d x}##, C and d arbitrary constants. C and d can be complex if you work with complex numbers.
It is a typical homework problem to show this.
 

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