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vsalgado1-Visitor
1-Visitor
November 12, 2013
Question

Equation From a graph?

Hi.

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

Untitled.png

10 replies

LucMeekes23-Emerald V
23-Emerald V
November 12, 2013

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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ValeryOchkov24-Ruby IV
24-Ruby IV
November 12, 2013

One way to get points from graph:

http://twt.mpei.ac.ru/TTHB/5/3/3_05_CC_Plot_Vectors.gif

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    Werner_E
    Werner_E25-Diamond I
    25-Diamond I
    November 12, 2013

    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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    VladimirN24-Ruby IV
    24-Ruby IV
    November 12, 2013

    Hi,

    Please attach your Mathcad Prime worksheet.

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    Werner_E
    Werner_E25-Diamond I
    25-Diamond I
    November 12, 2013

    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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    ValeryOchkov24-Ruby IV
    24-Ruby IV
    November 12, 2013

    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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    Werner_E
    Werner_E25-Diamond I
    25-Diamond I
    November 12, 2013

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

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    IRstuff1-Visitor
    1-Visitor
    November 13, 2013

    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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    Werner_E
    Werner_E25-Diamond I
    25-Diamond I
    November 13, 2013

    Getting the data is the first order of business.

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

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