VeLa filter on Phase gives strange result

[mpyat2]

Try the following VeLa filter: Phase >-0.1. ALL points will be selected.

[dbenn]

Hi @mpyat2. This seemingly odd result is due to the fact that every observation in a phase plot has:

• standard phase (or just phase), with range 0 to 1
• previous cycle phase, with range -1 to 0
  • in particular, previous cycle phase is standard phase - 1

In VeLa, when you ask for phase, you're getting standard phase.

If your filter is changed to phase > 0.9, the result you seek will be achieved.

Make sense?

Some possibilities:

• document that 0 < phase < 1?
• split phase into standard and previous cycle phase?

Previous cycle phase is a convenience to allow phase plots to show a representative phased light curve by placing two identical phase plots together. It's a visual aid more than anything.

We could try to combine standard and previous cycle into phase for filtering purposes, but that would require some thought.

[mpyat2]

Hi @dbenn, Well, I think it's enough to document that phase > 0 and phase < 1, at least for now. So, if anyone wants to filter for a phase in [-0.1 .. 0.1], she/he can write:

phase <0.1 or phase >0.9

[dbenn]

Added this at the end of the phase plots section:

Note that for filters (see Filtering Observations section) where the value of the observation's phase is sought, the range of phase values to be specified is from 0 to 1, the so-called standard phase. The so-called previous cycle phase value from -1 to 0 cannot be specified within a filter. So, for example, to create a filter that includes observations in the apparent phase plot range from -0.1 to 0.1, the VeLa filter expression phase < 0.1 or phase > 0.9 could be used.

[dbenn]

@mpyat2, I've changed the user manual text like so (with better use of bold/italic and font change)

Note that for filters (see Filtering Observations section) where the value of the observation's phase is sought, the range of phase values from 0 to 1 on the phase plot is the so-called standard phase or simply, the phase. The so-called previous cycle phase value is defined as:

1 - standard phase

and occupies the range from -1 to 0 on the phase plot. Selecting an observation via a filter with a particular phase, will also select the observation with the corresponding previous cycle phase, since this corresponds to the same observation.

A Simple Filter (View → Simple Filter dialog) can express the equivalent of this VeLa filter (View → VeLa Filter):

phase > 0.69 and phase < 0.71

but not this one:

(standardphase > 0.69 and standardphase < 0.71) or (previouscyclephase > -0.81 and previouscyclephase < -0.79)

Simple Filters do not allow disjunction (“or”). Only conjunction (and) between filter expression terms.

So, Simple Filters allow only phase to be specified (range 0 to 1), while VeLa filter expressions can contain the variables phase, standardphase and/or previouscyclephase.

[mpyat2]

@dbenn , sounds good!