[Aavso-photometry] Peranso vs Minima V2.3 question

[Michael Koppelman]

We're physicists, Michael, so 3.7 ~ 3.

:)

Seriously, though, your software and Minima's might have used similar  
techniques or libraries such that more of your calculations are  
similar. It is possible that you are both doing it wrong and Peranso  
is doing it right! But, Dear Reader, when in doubt Dr. Newberry is  
right and I am wrong. :)

Also, one must, in general, resist the temptation to just do a  
statistical average of these results since they are not truly  
independent.

M.



On Feb 17, 2009, at 3:52 PM, Michael Newberry wrote:

> Hi Michael,
>
> You have a good point and I appreciate what you are saying. But the  
> situation is a little more complex. The difference between his  
> Peranso and Minima values is 0.00016 day. The uncertainty reported  
> by Minima is sigma=0.00007 and that by Peranso is sigma=0.000045. I  
> got sigma=0.000065. Using the Minima sigma makes them 2.3 sigmas  
> apart but using the Peranso sigma makes them 3.7 sigmas apart. My  
> value and its uncertainty agree with Minima to beyond 5 places,  
> despite our implementations of the KvW algorithm being independent.
>
> In this case we are talking comparing small differences of 6 seconds  
> or 14 seconds. But it would be useful to know two things: 1) whether  
> a difference of this order is typical or it is usually larger or  
> smaller, and 2) whether the difference is random or systematic. In  
> other words, if, on multiple tests, Minima is sometimes higher and  
> other times lower than Peranso, and by similar amounts, then you can  
> say they are basically giving similar results within random  
> differences (which is what you said). On the other hand, if one had  
> a tendency to give values that were typically higher or lower than  
> the other, then there would be a systematic error that needs to be  
> addressed---as in, who's error is it?
>
> Michael Newberry
>
> ----- Original Message ----- From: "Michael Koppelman" <michael at slackerastronomy.org 
> >
> To: "Michael Newberry" <mnewberry at mirametrics.com>
> Cc: "Yenal Ogmen" <yenalogmen at yahoo.com>; <aavso-photometry at mira.aavso.org 
> >
> Sent: Tuesday, February 17, 2009 2:21 PM
> Subject: Re: [Aavso-photometry] Peranso vs Minima V2.3 question
>
>
>> My first reaction to Yenal's original email was: welcome to the  
>> world  of computational physics! There are many factors which can  
>> make  different implementations of the same algorithms vary, many  
>> of which  Michael mentioned.
>>
>> The error reported for Minima (as an example) was 0.00007 or about  
>> 6 seconds. The difference between Minima and Peranso is about 14   
>> seconds, which is ~2 sigma of the Minima result. So they agree!  
>> You  could use any of the results and be fine since they all fall  
>> within 3x  of the uncertainty. Your ToM is never known better than  
>> your  uncertainty (of course).
>>
>> A long time ago I tried to write my own ToM finding algorithm and  
>> it failed miserably. Another method that has served me well is  
>> curve- fitting with polynomials or some other function.
>>
>> Cheers,
>> M.
>>
>>
>> On Feb 17, 2009, at 1:14 PM, Michael Newberry wrote:
>>
>>> In general, using the same algorithm in different software does  
>>> not assure that the result will be the same.
>>
>