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11-12-2013
01:09 AM

11-12-2013
01:09 AM

Equation From a graph?

Hi.

I want to know how can I get the equation from this graph

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10 REPLIES 10

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11-12-2013
02:08 AM

11-12-2013
02:08 AM

Re: Equation From a graph?

Valentin,

You cannot get 'the' equation, but it is possible to get an approximate or best fit, provided that you have the data points.

Look up 'curve fitting' in the manual or help section of Mathcad. Focus on functions like regress() or any of the xxxfit() functions.

success!

Luc

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11-12-2013
05:04 AM

11-12-2013
05:04 AM

Re: Equation From a graph?

Hi,

Please attach your Mathcad Prime worksheet.

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11-12-2013
06:26 AM

11-12-2013
06:26 AM

Re: Equation From a graph?

You won't get THE equation. All you have is a number of points, so there are an infinite number of different equations possible. One of them could be a polynomial of n-1 th order if you have a datavector of n points. But of course you can also find logarithmic, exponential and other types of function or combinations of them which include all of your points. You have the choice between exact interpolation or approximation.

As valery wrote - attach you sheet, show what you have done so far and tell us as precise as possible what the intent is.

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11-12-2013
10:12 AM

11-12-2013
10:12 AM

Re: Equation From a graph?

One way to get points from graph:

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11-12-2013
11:43 AM

11-12-2013
11:43 AM

Re: Equation From a graph?

As far as we can see from the screenshot provided, Valentin does not need to digitize a plot as he already has the coordinates of the points in the matrix A. What he wants to find is an equation.

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11-12-2013
12:56 PM

11-12-2013
12:56 PM

Re: Equation From a graph?

Werner Exinger wrote:

But of course you can also find logarithmic, exponential and other types of function or combinations of them which include all of your points.

See the attach here http://communities.ptc.com/message/152121#152121

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11-12-2013
01:28 PM

11-12-2013
01:28 PM

Re: Equation From a graph?

From the screenshot Valentin provided it seems that he already has his points, he is searching THE(???) equation, not digitization.

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11-12-2013
07:23 PM

11-12-2013
07:23 PM

Re: Equation From a graph?

Getting the data is the first order of business. The cited thread mentions, I think, a program called Tracer, which, on a good day, will trace a picture of a graph and provide an ordered list of coordinates for points on the curve. One version can be downloaded through here https://sites.google.com/site/kalypsosimulation/Home/data-analysis-software-1

I haven't tried this particular version; I generally use 1.7, because there were some annoyances in 2.0.0, which might have been fixed in this version.

TTFN

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11-12-2013
08:01 PM

11-12-2013
08:01 PM

Re: Equation From a graph?

Getting the data is the first order of business.

Yes, but it looks like that job was already done.