What Are the Theoretical Forms for f(.) and g(.)?

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Discussion Overview

The discussion revolves around the theoretical forms of two functions, f(.) and g(.), defined by the identity f(cx) = k - g(x), where c and k are real-valued constants. Participants explore the implications of this identity and propose potential forms for the functions, considering various mathematical properties and relationships.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that f(.) and g(.) might be logarithmic functions, seeking analytical proof or counterexamples to this hypothesis.
  • One participant questions the meaning of the identity condition, suggesting that it implies a relationship that may limit the forms of f(.) and g(.).
  • Another participant argues that the identity does not restrict the forms of the functions significantly, proposing that g(x) can be expressed in terms of f(cx) and vice versa.
  • There is a suggestion that the constants c and k could be incorporated into the definitions of the functions, potentially affecting their forms.
  • A participant mentions the existence of experimental data that could inform the theoretical forms of f(.) and g(.), noting that while many functions may fit the data numerically, the challenge lies in deriving a theoretical model.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the identity condition and the potential forms of the functions. There is no consensus on the specific forms of f(.) and g(.), and the discussion remains unresolved regarding their theoretical representations.

Contextual Notes

Participants acknowledge that the relationship between f(.) and g(.) is complex and may depend on the definitions of the constants involved. The discussion highlights the limitations of the provided information and the challenges in deriving theoretical forms from experimental data.

ssd
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Given that
1/ f(cx) = k - g(x) and
2/ the above is an identity,
where f(.) and g(.) are two functions
and c, k are real valued constants.

The problem is to infer upon the types of f(.) and g(.).
I have a hunch that f(.) and g(.) are logarithimic functions. Can anyone provide any analytical proof or counter example?
 
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What do you mean by "2/above is an identity"?
 
Surely there should be some mention of c on the RHS? Otherwise only constant functions work.

For f(c)=f(c.1)=k-g(1) for all c, i.e. f is identically equal to k-g(1), whatever g(1) is. And then g(x)=k-f(cx)=g(1), for all x.
 
Well, making c part of the definition of g(x) would do.

The obvious choice is to take g(x) = k - 1/f(cx), for whatever definition of f(x) you wish; in other words, I don't think the condition limits the actual form of the functions in any way (except by relating one to the other). For example, if f(x) = x^2, then g(x) = k - 1/(cx)^2. And so on.

Edit: Oh, sorry, I read the original condition as 1/f(cx) = k - g(x). But the argument stays the same. Just take g(x) = k - f(cx). If f(x) = x^2, then g(x) = k - (cx)^2.

(Yet another edit:)
Or... (psychic powers for the win)... by his logarithmic hunch, the OP meant something like f(cx) = h(c) - g(x), with f(x), g(x), h(x) functions and c a constant.
 
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arildno said:
What do you mean by "2/above is an identity"?

We are given with two conditions. 1st condition is the expression given in point 1. The 2nd condition is given in point 2, which states that the expression given point 1 is an identity.
 
matt grime said:
Surely there should be some mention of c on the RHS?

'k' in RHS can involve 'c' in some suitable form. Similarly 'c' can involve 'k' in some form. Or, g(.) may contain c or f(.) may contain k... I don't really know. I know that 'k' and 'c' are two numerical constants obtained from an experiment, and they don't change with change of the study parameters of the experiment.
 
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Oh, it can, can it? Are there any other things you've not mentioned?
 
matt grime said:
Oh, it can, can it? Are there any other things you've not mentioned?

No, nothing is appearing in my mind at this moment except that f(.) and g(.) are real valued.
 
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Is there a table of numeric results for f() and g(), coming out of experiments, that you can post?
 
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Dodo said:
Is there a table of numeric results for f() and g(), coming out of experiments, that you can post?

Yes it is there. In fact there are a number of such tables obtained from different experiment stations by different scientiests under similar set up. The values are small in number (like 10 to 12) in one set. Practically may functions fit (numerically) the data (of one set) well. There are moderate variations in data from different stations. But the problem is to find a theoretical form. One has to infer only on the basis of information I gave already. I (we) have theoritically simplified the work upto this. The usual forms of the expressions and the method (using which c & k are found in current practice) are really complicated.
 
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