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

[Michael Newberry]

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.
>
>