Finding bend(maxima/minima) in plotted curve

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Discussion Overview

The discussion revolves around identifying bends, maxima, and minima in plotted curves, particularly in the context of pump curves. Participants explore methods for analyzing the slope of curves to determine local extrema and the implications of slope changes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that changes in slope can indicate the presence of bends or local maxima/minima, questioning how significant these changes should be.
  • Another participant states that a change in the sign of the slope typically indicates a local maximum or minimum.
  • A different viewpoint raises the possibility that a curve may not reverse direction but could still have a steeper slope, leading to confusion about identifying extrema.
  • Participants discuss the characteristics of sine waves, noting that they exhibit multiple local maxima and minima due to oscillation.
  • One participant introduces the concept of vertical asymptotes in relation to pump curves, suggesting that these may influence the analysis of the curve's behavior.
  • There is uncertainty about the order of the equation representing the pump curve, with some participants proposing it could be a first or second order equation.
  • Participants express a need for visual aids, such as images of pump curves, to facilitate understanding and discussion.
  • One participant shares a link to typical pump curves, noting the absence of maxima or minima but the presence of a vertical asymptote.
  • There is a request for guidance on determining the degree of curve equations and solving for these equations based on the plotted data.

Areas of Agreement / Disagreement

Participants express differing views on how to identify bends and extrema in curves, particularly regarding the significance of slope changes and the characteristics of pump curves. The discussion remains unresolved with multiple competing perspectives on these topics.

Contextual Notes

There are limitations in the discussion regarding the assumptions about curve behavior, the definitions of terms like "vertical asymptote," and the mathematical steps necessary to determine curve equations. These aspects remain unresolved.

KN2007
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I want to write a computer program or subroutine to find the number of bends or maxima/minima on a plotted curve of points. How can I use the points defining the curve to do this. I would expect that the change in slope would tell me, but how significant of a change should I be looking for? I think this is the right approach. Any help would be appreciated.
 
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Well when the slope changes sign is how we usually tell there is a local maximum or minimum.
 
Well, what if the curve does not reverse directions, but only has a steeper slope?
 
Then the slope will not have changed sign. I'm not sure what you mean by a curve reversing direction. Could you clarify?
 
Well, I suppose in a sine wave the curve oscillates and reverses direction.
 
Ok well a sine wave consists of a lot of local maxima and minima. at these maximum and minimum points the gradient of the curve changes sign. That would indicate the curve reversing direction as you put it. If the curve doesn't reverse direction but the gradient gets steeper then there is no local maximum or minimum. Perhaps you are talking of a vertical asymptote however?
 
Perhaps it is a vertical asymptote. Actually it is a pump curve. I suppose this would simply be a 1st order curve or curve of one degree still?

OK, yes, I suppose a pump curve would be a vertical asymptote. So how would I find the order of the equation based on the plot. Should I assume it to be a second order equation?
 
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I think you'll need an engineer to help you with that. I'm not sure what a pump curve is. From having a quick google it doesn't look as if they have any vertical asymptotes.
 
OK, it looks like it will be a 1st order or degree equation. Maybe it will curve or maybe it will be straight, but it probably should not have more than one degree or order.
 
  • #10
It might help if you could posta picture of the curve you are trying to describe.
 
  • #11
Yes, I was thinking of posting some sample curves, but I could not figure out how to do it. How do I upload a file here? Would pasting it work?
 
  • #12
You can host an image on an image hosting site and use image tags, or there is a facility to upload files but their size is limited and they need to be approved by a mentor before anyone can see them which sometimes takes a while.
 
  • #13
OK, here is the link to the image for some typical pump curves.

http://blogpost.imageshack.us/blogpost/postblog.php?id=img260/5971/typicalpumpcurvesjuly29ty6.jpg

I think you can access it. Please let me know.
 
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  • #14
KN2007 said:
OK, here is the link to the image for some typical pump curves.

http://blogpost.imageshack.us/blogpost/postblog.php?id=img260/5971/typicalpumpcurvesjuly29ty6.jpg

I think you can access it. Please let me know.

These graphs do not have any maxima or minima. They do, however, have a vertical asymptote towards the right of the graph.
 
Last edited by a moderator:
  • #15
So how can I determine the degree of the curve equations and better yet solve for the equations of the curves?
 

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