I'm using Matlab's curve fitting app, When I select Power fitting it returns values which perfectly describe the data but when I use the custom equation and enter ax^b as the equation it returns very bad coefficients. Shouldn't the results be the same?
I need to fit a data to a $ax^{-6} + bx^{-4} + cx^{-2}$ function so I need to use custom equation.
EDIT: Added the screenshots.