What does the Centroid of area under Rate vs Time plot represent?

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Discussion Overview

The discussion centers on the interpretation of the centroid of the area under a rate vs time plot, exploring its potential physical significance and how it can be used for comparison between different plots. Participants consider various attributes that could distinguish the characteristics of the plots, including variance, average rate, and the shape of the area under the curve.

Discussion Character

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

Main Points Raised

  • One participant questions whether the centroid of the area under the rate vs time plot represents anything physical and seeks a method for comparison beyond cumulative volume.
  • Another participant suggests that the rate coordinate of the centroid could represent the mean square of the rate divided by the mean rate, indicating a measure of variance.
  • A participant expresses interest in using the centroid for comparison but notes that variance may not be helpful for distinguishing the value of the rate.
  • There is a discussion about the need to identify what specific attribute participants are looking for in the comparison, as some options like average rate and peak rate are dismissed.
  • One participant proposes a method to distinguish between higher rates over shorter times versus lower rates over longer times, suggesting that the shape of the area under the curve could be significant.
  • Another participant questions the reluctance to use the highest average rate as a comparison metric.
  • A mathematical expression is presented to argue that a higher average rate applied over a shorter time could be considered "better," although the desirability of this perspective is questioned without knowing the intended application.

Areas of Agreement / Disagreement

Participants express differing views on the attributes that should be used for comparison, with no consensus reached on the best approach or interpretation of the centroid's significance.

Contextual Notes

Participants have not settled on the definitions of key terms such as "better" in the context of rate comparisons, and there are unresolved questions regarding the physical implications of the centroid in relation to the area under the curve.

geetar_king
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What does the "Centroid" of area under Rate vs Time plot represent?

Does the 'centroid' of the area under a rate vs time plot represent anything?

I have a bunch of rate vs time plots and was trying to think of a way to compare them, other than just cumulative volume which is area under the rate vs time plot. Would centroid somehow weigh in on the rate?

Wondering if this represents anything physical...

Cheers
 
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I think the rate co-ordinate of the centroid will be the mean square of the rate divided by the mean rate. So it gives a measure of variance. Nothing springs to mind for the time co-ordinate.
 


Thanks haruspex, if the rate coordinate of the centroid represents the variance, then I could use that for comparison.

I was hoping to find something for comparison to weigh in on the value of the rate. If higher rate = better, variance won't help me in comparison. I don't want average rate because you lose detail of amount of time spent at higher vs lower rate

I wonder if area moment of inertia of the centroid would give me this? or some sort of weighted average maybe.
 


You need to decide what attribute it is you're looking for. You say say it's not the average rate, or the peak rate, or the variance... so what is it?
 


I want some attribute to distinguish higher rates in a shorter amount of time versus lower rates for a long amount of time. Eg tall skinny area under curve vs short and wide area.

I'm not sure how to do this without simply looking for shortest time, or highest avg rate.
 


OK, but why do you not want to use highest average rate?
 


If it's desirable to have a high average rate and a short amount of time, how about

(average rate) × (1/Δt)

= \frac{\left( \frac{\int R \ dt}{\Delta t} \right)}{\Delta t} = \frac{\int R \ dt}{(\Delta t)^2}

That would mean the same rate applied over a short time is "better" than the same rate applied over a long time. Not sure if that is desirable, without knowing what this is supposed to be used for.
 

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