Discrete and continuous problems

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    Continuous Discrete
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Discussion Overview

The discussion revolves around the transition from discrete summation to continuous integration, specifically exploring the conditions under which a sum can be represented as an integral. Participants examine the implications of defining a function for non-integer values and the relationship between summation and integration in calculus.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the conditions necessary to convert a sum of discrete terms into an integral, particularly when n approaches infinity.
  • Another participant notes that the ability to make this conversion heavily depends on the definition of the function a(x) for non-integer values.
  • A different participant suggests that the summation can be approximated by an integral if the function has a consistent positive or negative derivative across its domain and lacks critical points.
  • It is mentioned that using linear interpolation between integer values can yield a function suitable for integration that aligns with the summation results.

Areas of Agreement / Disagreement

Participants express differing views on the conditions required for the transition from summation to integration, indicating that multiple competing perspectives remain without a consensus on the matter.

Contextual Notes

The discussion highlights the importance of defining the function a(x) appropriately for non-integer values, as well as the potential limitations of using linear interpolation in this context.

haiha
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Hi all,

There are some dificult problems with discrete argument n that will be very easy if I can change it to continuous argument x. But I do not know what is the condition for that.
For example: to calculate the sum of a1+a2 +a3+...an. when n goes to infinity, can I make it as S=integral of a(x) from xo to infinity ?

Thanks
 
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For example: to calculate the sum of a1+a2 +a3+...an. when n goes to infinity, can I make it as S=integral of a(x) from xo to infinity ?
It depends very much on how you define a(x) for x not an integer.
 
Could you please explain more about that.
I just think the sume of An is similar to the way we calculate the integral in calculus. I mean Sum(An) = a1*d+a2*d+...an*d where d equals 1. When we calculate to rather large integer n, then d = 1 is small enough to have adequate accuracy.
May I think that this can happen only when f(x) must have positive (or negartive) derivative all over the domain, and f(x) must also have no critical points. ?
 
Since a(x) has to be defined for x not integer, the integral will depend on precisely how it is defined. For example, linear interpolation between the integer values will give you a function which can be integrated to give the same result as the summation.
 

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