I need to find a equation that can be used to describe a graph. I have attached a file that contains more details. Is there any curve fitting software that I can use? I have tried solver, trendline option in excel, unfortunately, failed to get any fitting equation.
Can you tell me more about this set of data?
To me it looks like that the data does not fit within the definition of a mathematical function, as a function cannot have more than one value of y for every value of x. Your data has more than one value of y for each x value hence it does not fit within the description of a function. Most regression tools work on the assumption that the data can be fitted into a function. Since your data does not obey that assumption, excel fails to fit a trendline for you. But I may be able to help out if you give me more details about your data.
Regards,
Ali
Alireza Meghdadi Thanks a lot for your reply. This set of data presents the relationship between stress ratio and dilatancy. I am attaching some figures for your reference. I hope it helps.
Regards
Towhid
You have to first sort the columns x and the corresponding values of the 2-nd column y. It is easily done with excel sort function. Then you can easily plot a function y=f(x), and then add a trendline using excel add-on utility.
The result is the best fit (i) polynomial of the 4-th order with R^2=0.918, or (ii) moving average with period 2. See attached file.
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