Note from 1 May 2022

If I have a graph like this, is there a standard mathematical way to identify each strait segment and the formula it is based on?

A graph composed of a series of strait lines

8 reactions

Dr Floyd 🇺🇸🇬🇧🇫🇷
Yes. y=ax+b with different à and b for each interval. The exception is the vertical line which is x=c over an interval in y
- 1 May 2022, 18:45
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Nicolas Hoizey
I don't need the vertical line.

But I know the generic formula of a strait line, what I need help to find is each a and b… 😅
- 1 May 2022, 18:47
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Dr Floyd 🇺🇸🇬🇧🇫🇷
You can compute a and b given the x and y of each end. a = (y2-y1)/(x2-x1) b = y1 - ax1
- 1 May 2022, 18:52
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Nicolas Hoizey
Ok, but is there a way to find these "ends"?
- 1 May 2022, 19:09
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Dr Floyd 🇺🇸🇬🇧🇫🇷
If you only have the graph then you can only read them off the graph - hard to be exact
- 1 May 2022, 19:11
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Nicolas Hoizey
I will be generating a lot of graphs, so I need an automated solution, I can’t use my eyes. 😅

Thanks for trying to help anyway! 🙏
- 1 May 2022, 19:18
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Pascal C
Tu as les data ?
Si oui (et que tu as bien x = c de manière certaine) tu peux identifier les intervalles sur lesquels calculer la pente
- 1 May 2022, 19:56
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Eric Portis
.@ausi’s logic for writing sizes attributes might be helpful: github.com/ausi/respimage…

Basically, start at one side of the graph, Δx by some step value, determine a&b based on observed y, keep stepping by Δx, and use those a&b vals to predict each y. (1/2)
- 2 May 2022, 17:03
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