[proFit-list] How can we change the behaviours of x and x0 in power law fitting?

[Kurt Sutter]

What my colleague wrote below is correct. You can use x instead of x0, you just have to swap the sign.

Note: In more general cases, there may be situations where a built-in function does not work for you. In that case, just define your own function. In your case, you could e.g. define a function like this


##function PowerLaw

def PowerLaw(x, t, const, m, n):
    return const + m * (t-x)**n

(This is the Python version.) Here, x takes the role of x0 of the built-in function, and t takes the role of x of the built-in function.

Best regards

Kurt Sutter
QuantumSoft


On 27 Feb 2012, at 2:31, pro Fit support wrote:

> x and x0 are mathematically equivalent in the definition of the function, they differ only by their signs.
> 
> Therefore, you should just keep using "x" as the default input and use x0 as the fitting parameter.
> 
> (but to still answer the question: the "x" parameter in pro Fit functions is wired a little bit differently for reasons of speed, and this is why it can't be made into a fittable parameter when the default input is another one. But this apparent limitation is not important because most functions depend on "(x-x0)")
> 
> pro Fit support
> profit at quansoft.com
> 
> 
> On Feb 27, 2012, at 1:56 AM, riki wrote:
> 
>> Hi all,
>> 
>> In power law fitting, I want to use "x0" parameter as the Default input which we can do in Parameters panel. But if I want to 
>> use "x" parameter for fitting, we could not because Use for fitting button is diabled for "x". How can we get rid of this 
>> problem?
>> 
>> Kind Regards,
>> Riki
>> 
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