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B Creating Equation Based on Data Set of x,y Values

  1. Nov 15, 2016 #1
    I'm attempting to reclaim lost knowledge... hopefully this works. I would like to take a data set I have x,y values and project the trend beyond the (10) values I currently have. For example, I have a graph with (10) values for x and y, but would like to graph the trend created by values 1-10 to values 11-15.

    I recall learning how to derive an equation to represent the data set but how no idea how I used to to it. Need some help on this one. I'm sure there are other ways to do this that I haven't thought of and wouldn't mind suggestions.

    PS, I know I could create a simple linear equation by eyeballing the best fitting slope, but would like to be more accurate as the trend is not always linear.
     
  2. jcsd
  3. Nov 15, 2016 #2

    mfb

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    If the trend is not linear and you want to extrapolate beyond the outermost data points, you'll need some other model ("it is linear" is a model as well). There are many possible models, the best one will depend on your data source. A parabola, an exponential function, a square root, a logarithm, some combination of those, ....
     
  4. Nov 15, 2016 #3
    In that case I would say the tendency is for logarithmic and exponential. Could you suggest an example model for logarithmic?
     
  5. Nov 15, 2016 #4

    mfb

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    y=c*log(x)?
    y=c*log(x+d)?
    y=c*log(x+d)+e?
     
  6. Nov 16, 2016 #5

    Svein

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    As usual, it depends. If the data set is a set of measurements, I would use a form of regression (linear, quadratic, exponential...). If the data is a set of calculated values, you can create a polynomial expression that passes exactly through your data points (but that expression is usually useless in predicting values outside the original data set). I suggest you peruse https://en.wikipedia.org/wiki/Curve_fitting.
     
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