Linear and power fitting of original and transformed data not reproducible

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Xen
Xen 2020-1-30
评论： Vladimir Sovkov 2020-1-30
I am fitting two variables that seem to have a power relationship (y=a*x^b). If I log-transform both variables, they should have a linear relationship (ln(y) = c*ln(x) + d. Notice that b=c and ln(a)=d. However, when I fit the power and linear equation to these, respectively, the estimated coefficients do not satisfy these relationships. Expectedly, R-square is also different. I tried changing the fit options and didn't manage to make the two fittings equivalent. Has anyone any idea why this happens?
PS. fitting in excel is satisfying these relationships and I get identical values
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Xen
Xen 2020-1-30
Thanks for the reply Vladimir. The weights of y are by default ones(n,1). How would you recompute the weights for ln(y)?
Vladimir Sovkov
Vladimir Sovkov 2020-1-30
The weights must be , however, it is better to check the documentation of the tool you are using.

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