Pomoc laiku

[all_this_time]

Ja ne znam nista o astronomiji, a moram da uradim seminarski iz data mininga u kom obradjujem podatke vezane za astronomiju. Mislim da je pametnije da okacim ceo tekst nego da ga prepricavam pa negde pogresim. Ovo je dakle opis datoteke E.dat - koju takodje imam, ona u sebi sadrzi 27220 redova od cega 27204 su brojevi u intervalu -0.7 do 0.7 i 16 redova koji te podatke odvajaju u 17 celina. Moj problem je tabela iz donjeg teksta. Prve dve kolone su u redu, tj razumem ih, i fajl E.dat zaista sadrzi onoliko brojeva u svakoj celini koliko pise u II koloni (Jedino zbunjujuce u vezi toga je sto na pocetku donjeg opisa pise da E.dat sadrzi 27704 merenja, dok ona ustvari sadrzi 27204, ali pretpostavljam da je to samo greska). Ono sto ne razumem je u kom formatu je zapisana treca kolona - 'starting time'. Meni bi mnogo znacilo da svakoj tacki iz svake celine dodelim vreme merenja. U tekstu pise da je svaka sledeca tacka merena sa razmakom od 10 sekundi (ako dobro razumem), ali kako ne znam da protumacim pocetno vreme, ne znam ni kako da na pocetno vreme dodajem tih 10 sekundi.

Svaka pomoc bi mi dobrodosla:)



Datoteka sa materijalom: E.dat: Astrophysical data
Original Description:
E.dat (27704 points)
This is a set of measurements of the light curve (time variation of the intensity) of the
variable white dwarf star PG1159-035 during March 1989. It was recorded by the Whole Earth
Telescope (a coordinated group of telescopes distributed around the earth that permits the
continuous observation of an astronomical object) and submitted by James Dixson and Don
Winget of the Department of Astronomy and the McDonald Observatory of the University of
Texas at Austin. The telescope is described in an article in The Astrophysical Journal
(361), p. 309-317 (1990), and the measurements on PG1159-035 will be described in an
article scheduled for the September 1 issue of the Astrophysical Journal. The observations
were made of PG1159-035 and a nonvariable comparison star. A polynomial was fit to the
light curve of the comparison star, and then this polynomial was used to normalize the
PG1159-035 signal to remove changes due to varying extinction (light absorption) and
differing telescope properties.

The samples in the files are all integrations spaced at 10 second intervals. The number
of points and starting times of the parts are

   part  points  start time
   ----  ------  ----------
     1,   618,   521048.7
     2,   1256,  526881.9
     3,   1222,  539951.9
     4,   980,   550941.5
     5,   550,   559402.8
     6,   1554,  566422.8
     7,   1937,  585517.5
     8,   2496,  613164.2
     9,   1941,  633834.8
     10,  1472,  647065.1
     11,  2605,  671536.7
     12,  1549,  699206.4
     13,  2568,  707915.6
     14,  2602,  731247.2
     15,  673,   764048.0
     16,  1512,  774058.0
     17,  1669,  794053.6

where the times are in seconds from the beginning of the observational run.

The intensity variations of the star arise from the excited modes, which are spherical harmonics.
For a given mode Y_(klm), for each l value there will be 2l+1 m modes. For a fixed star the m modes
have the same frequency; rotation of the star and magnetic fields split this degeneracy.
The two main questions that it is hoped these data will help answer are:


How many modes are excited? The W.E.T. group believes that this number is very large (on the order of 100).


Do the excited modes of the star interact, and what is the form of this interaction (i.e., is it nonlinear)?
Reason for choice:
Noisy data
Both this set and set A represent the optical oscillations of a physical system, but unlike set A, which has
very little noise, the measurement process for these data is much noisier. These observations are all that
is available, and in fact represent a tremendous experimental effort to collect them, and so any insight
into this system must come from the time series analysis.


Discontinuous data
The method of collection naturally partitions the data into separated observations, and so a successful
analysis must combine the information from these segments.


Probably linear, possibly nonlinear
Unlike many of the time series problems in the recent literature (such as the optical oscillations in set A),
these data represent a difficult observational question about the behavior of a primarily linear system.
The initial question here is in principle simple: assuming linear spherical modes, how many of them can
be recognized above the experimental background? A followup question is much harder: are there nonlinear
interactions among the modes?

[Ljubo]

Trebala si okaciti ili dati link i za E-dat fajl.

U tekstu pise da je svaka sledeca tacka merena sa razmakom od 10 sekundi

Greška! podaci su snimljeni ekspozicijom (trajanjem snimanja) od po 10 sekundi, dok su sami trenuci vremena dati u odnosu na pocetno posmatranje, i traje u sekundama.

Osnovni grafik (na Wikipediji imaš linkove kako su napravljeni i segmentni grafikoni za pomenutu zvijezdu), konstruiši ovako:

Na apscisi uzmi da ti je početni trenutak vremena 520 000 sekundi, podijeli vremensku osu zatim na podioke od po, recimo, 20 000 sekundi, sve do 800 000. Možeš i resetovati brojač sekundi na nula počevši od, recimo, 520 000, i uzeti pomenute intervale od 20 000 sekundi (ili pisati samo po 20, a na apscisi obiljeziti t (10 na 3 sek).
Na ordinati nanesi intenzitet u tačkama (možeš početi od nule, ili od 600 tačaka, svejedno!).
Dobijene pikove spoji u tvom Data Miningu, i to je graf intenzitet vs. period.

Zadnji dio teksta odnosi se na prezentaciju mogućeg scenarija varijabilnosti intenziteta pomenute zvijezde. Ako preskočimo fizički dio (harmonici koji su degenerisani zvjezdanom rotacijom i magnetnim poljem), ono što bi trebalo utvrditi je da li postoji linearnost u promjenama pikova u toku vremena, ili se radi o nepravilnim (nelinearnim promjenama), što se može pročitati ili naslutiti sa tvog grafa.