Equation of model

Hi Avon

It may be worth looking at a particular example. To reproduce the problem, can I ask you to post a sample dataset, DCDFT parameters, periods and number-of-harmonics selected to created the model?

Also, the program (in python, ...?) you're using to work with the VStar model equation would be good to look at.

Regards,

David

Hi Avon

Thanks. I'll have a look at this data.

To clarify, does the IDL code use the frequency from DCDFT and the Fourier Series coefficients A, B, C from a model (# of harmonics=1) created from that frequency in VStar?

Also, as an aside, is the data file from a particular source that might make a good candidate for an observation source plugin, or a personal format?

Regards,

David

Hi Avon

Apologies for the silence the last couple of days. I've been focussing on preparing a new VStar release before the Silly Season gets fully underway.

I just wanted to mention that:

1. As part of looking at this problem I ended up writing a Catalina Sky Survey observation source plugin for VStar. That will be available on the plugin library page when the new release is out (look for release announcement on this forum).
2. I haven't tracked down the cause of the offset issue you reported yet. It appears that you are able to compensate for this but we need to understand where the problem is introduced.

I will continue to look at this when I can. The next couple of weeks will be problematic in that regard however.

I have captured this problem in a SourceForge tracker item:

https://sourceforge.net/tracker/?func=detail&aid=3596907&group_id=263306&atid=1152052

Regards,

David

Hi Avon, all

Okay, so first: apologies for the long time since my last post to this thread. I was busy being a CHOICE course participant for the last few few weeks.

Second, I've reproduced your result by writing some R code, and I agree that the problem exists. The model equation generates a continuous curve that is offset (to the right) by a certain amount from both the observation data and the model data that the model equation purports to represent. So, this implies that the model function being generated by VStar is in error.

I've attached a bunch of files. They relate to your sample CSS data. Here's the raw and phase plots and model data points for a single period (196.783 days).

I also created a model (in VStar from DCDFT dialog) based upon that period and 4 harmonics (see 5f files below). Here's the phase plot with observations and model data points:

The attached files are:

• data.csv: the observations saved from VStar as CSV.
• model_f.csv: the single period model saved from VStar as CSV.
• model_5f.csv: the 5 period model saved from VStar as CSV.
• model_f.png: plot of observations (from data.csv), single period model data points, and single period model function.
• model_5f.png: plot of observations (from data.csv), 5 period model data points, and 5 period model function.
• model_plotter.R.txt (only has .txt suffix so I could attach it): R code that generates the last two plots.

Here are the two plots generated by the R code:

In both cases the offset of the function generated line plot from the observation and model data points is obvious.

Next step is to figure out what is apparently going wrong with model function generation.

David

I ran TS on the same data (converted to tab-separated form: data.tsv.txt, attached), generating a model for the 196.7829 day period.

The result is consistent with that from VStar. It would have been surprising if that weren't the case given that VStar's implementation is based upon TS.

The file ts_session.txt (attached) shows the TS run.

The following is from the end of the session output (data.ts.txt (attached)):

     Frequency     Period      Power  Amplitude      cos        sin       const

   0.005081741    196.7829     Fre01     0.3984    -0.3821     0.1128    13.0963

The file model_f_residuals.dat_.txt contains the residuals from the single-period model.

David

Hi Avon, all

Almost another month has elapsed since my last post on this topic!

Here's an update.

With reference to my previous post, the model (line fit) was plotted via the R code:

lines(jds, model(jds), col="blue")

giving:

In email correspondence, Matthew pointed out the need to use the same time-center of zero (or zero point) when plotting the model (blue line) as was used when the model was built. I looked at this and confirm that VStar (and TS) create a zero point and subtract it from JDs values in the range when building the Fourier series model. I'm looking further at the computation of the zero point.

Taking this into account, Avon's earlier comment about subtracting period/4 from the (zeroed) JDs gives the expected fit:

jds = jds-jd0

lines(jds+jd0-period/4, model(jds), col="blue")

where jd0 is a zero point constant (based upon, but not equal to, the first JD in the model range) subtracted from all JDs in the range before the model function is invoked on each JD (added back for the plot), and period is the fundamental period of the model, giving:

However, the same result can be obtained by subtracting period/8 without first subtracting a zero point from all JDs in the range:

lines(jds-period/8, model(jds), col="blue")

I'm continuing to look at the model creation code as I find the time.

Additional datasets and models of these datasets also need to be looked at to determine whether the findings based upon this sample dataset and model apply more generally.

David

Hi Avon, all

This bug is now fixed!

Thanks to Matt and Avon for their help in resolving this! Their comments guided me toward a solution.

The zero-point extracted during model creation was not being added back into the equation shown in the Analysis -> Models... dialog. Finding the right bits of the model creation code took awhile. 

One of the things that will be included in SourceForge and probably elsewhere (e.g. docs) now is an R script that will plot observation and model data (saved from VStar as data.csv and model.csv) and the model function as a line plot. Here it is:

 https://sourceforge.net/p/vstar/code/HEAD/tree/trunk/script/plot_model.R

I've attached files showing another example, using LX Cyg. One plot is from VStar, the other from the R script.

This fix, along with others, will be in a new release sometime in the next week or two.

David