Do Integral Properties of Functions Imply Independence from Variables?

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Discussion Overview

The discussion revolves around the implications of integral properties of two functions, f(x,y) and g(x,y), specifically whether the independence of the integral of their product from the variable x implies that both functions do not depend on x. The scope includes theoretical exploration of function properties and mathematical reasoning.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant questions whether the independence of the integral of f^n * g from x implies that both functions f and g are independent of x.
  • Another participant argues that if g(x,y) is zero for all x and y, then the integral will be constant regardless of f, suggesting that the independence does not necessarily imply independence of the functions themselves.
  • A third participant notes that if f^n * g is interpreted as composition, then g would need to be a vector, indicating a potential misunderstanding of the operations involved.
  • The original poster clarifies that f and g are scalar functions and that the multiplication is ordinary, asking if the statement holds without assuming trivial solutions where either function is zero.

Areas of Agreement / Disagreement

Participants do not reach a consensus. There are competing views regarding the implications of the integral's independence from x and the conditions under which the functions may or may not depend on x.

Contextual Notes

The discussion includes assumptions about the nature of the functions (scalar vs. vector) and the operations (composition vs. multiplication) that may affect the conclusions drawn. There is also a lack of resolution regarding the implications of the integral properties without trivial cases.

Heirot
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Hello,

let's say we have two functions of two variables: f(x,y) and g(x,y). Say we know that the sum / integral over all y's of f^n * g does not depend on x for every natural number n (and zero). Does that mean that f and g both don't depend on x?

Thanks
 
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Not necessarily. Let g(x,y)= 0 for all x and y. Then f^n*g (I assume you mean composition) is f^n(0) for all x and y so the sum/integral is a constant no matter what f is. If f^n*g is ordinary multiplication of functions, then f^n*g= 0 for all x and y and again, the integral is a constant no matter what f is.
 
If it's composition, then g better be a vector
 
Sorry for not being clear - f(x,y) and g(x,y) are scalar functions and * is ordinary multiplication. f^n is then f multiplied n times by itself. Now, if we don't assume the trivial null solution, f(x,y)=0 or g(x,y)=0, does my statement hold?
 

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