# Finding Multiple Values of Y with Input values of X using Graph

1. ## Finding Multiple Values of Y with Input values of X using Graph

Hi,
I have sample data based on which I have created a graph as provided in the attachments. Based on the current graph, I want to find a function or utilized the same graph to predict (intrapolate/extrapolate) y values based on random values of x. I am looking for a universal solution which could work on any kind of graph irrespective of shape.

Thanks for understanding and looking for your help Graph Snapshot.PNG  Register To Reply

2. ## Re: Finding Multiple Values of Y with Input values of X using Graph

I am looking for a universal solution which could work on any kind of graph irrespective of shape.
A very tall order, I'm not sure it is even possible.

The problem with your request is that different shaped graphs require different regression equations, and Excel (or other programming language) just cannot choose a regression equation for us*. With innumerable possible regression equations to choose from and different regression schemes (linear or non-linear or piecewise, least squares or maximum likelihood or others), it's at best a daunting task to program something truly universal.

So far the discussion has focused on regression type schemes. Another possibility is to use an interpolation algorithm (probably easiest to implement using Gnumeric's INTERPOLATION() function which can do both linear and spline interpolations. Unfortunately, Excel does not have a built in interpolation function). The main difficulty with interpolation algorithms is deciding how to extrapolate beyond the end points of the tabulated data. Again, coming to a universally applicable decision can be difficult.

IMO, it is impractical to expect a universal solution that will work in every possible scenario. So we, as programmers, need to decide what kinds of scenarios we expect to see, choose what regression equations/algorithms will be applicable to most of those scenarios, and implement those algorithms into our spreadsheet.

For other's information, this looks like an extension of this thread: https://www.excelforum.com/excel-gen...n-problem.html

* -- I'm sure someone who knows artificial intelligence might argue that he/she could set up an AI module that could do this, but I am assuming that such a programming task is beyond what any of us would want to try to piece together.  Register To Reply

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