[Ifeffit] negative amplitude

[Welter, Edmund]

Dear Wojciech,

I presume you mean the "amp_x" value, this topic was discussed in 
January 07 on this list and Scott Calvin and Kelly Shelly gave useful 
hints (The subject was "is there a physical meaning to a negative S02") 
It all boils down to the question what happens if you multiply sin(x) 
with -1. So it seems that the model you use in your FEFF calculation is 
off by a half an oscillation.

regards,
Edmund Welter


Wojciech Starosta wrote:
>      Sorry if it is FAQ. But I spent some time on fitting without
> success and have not found answer to this.
> 
>   Does anybody could explain me if negative value of amplitude has any
> sense. I can get beautiful plot after fit, but unfortunately the message
> appear concerning  negative value of amplitude (amplitudes). How to
> avoid it. Any written material will be very helpful.
>    I know that I can define amplitude as squared value of new variable.
> But sometimes it does not work. Ifeffit stops with message that value of
> this variable cannot be determined
> 
>    With the best regards
> 
> 
> Wojtek Starosta
> Institute of Nuclear Chemistry and Technology
> 03-195 Warsaw, Dorodna 16
> Institute of Nuclear Chemistry and Technology
> 
> 
>     
>    
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> 
> 
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