Hi all
I have a set of data whose scatter plot shows a very nice power
relationship. My problem is when I fit a Power Trend Line in an Excel
spreadsheet, I get the model y= 44.23x^2.06 with an R square value of 0.72.
Now, if I input the same data into R and use
model< -nls(y~ a*x^b , trace=TRUE, data= my_data, start = c(a=40, b=2)) I
get a solution with a = 246.29 and b = 1.51. I have tried several starting
values and this what I always get. I was expecting to get a value of a
close to 44 and that of b close to 2. Why are these values of a and b
so different from those Excel gave me. Also the R square value for the nls
model is as low as 0.41. What have I done wrong here? Please help. Thanks
in advance
David
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