Finding bend(maxima/minima) in plotted curve

[KN2007]

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.

 

[Kurdt]

Well when the slope changes sign is how we usually tell there is a local maximum or minimum.

 

[KN2007]

Well, what if the curve does not reverse directions, but only has a steeper slope?

 

[Kurdt]

Then the slope will not have changed sign. I'm not sure what you mean by a curve reversing direction. Could you clarify?

 

[KN2007]

Well, I suppose in a sine wave the curve oscillates and reverses direction.

 

[Kurdt]

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 verticle asymptote however?

 

[KN2007]

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?

 

[Kurdt]

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 verticle asymptotes.

 

[KN2007]

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.

 

[Kurdt]

It might help if you could posta picture of the curve you are trying to describe.

 

[KN2007]

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?

 

[Kurdt]

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.

 

[KN2007]

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.

 

[cristo]

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.

 

[KN2007]

So how can I determine the degree of the curve equations and better yet solve for the equations of the curves?