[daip] Question about the relation between DPFU and Poly in GC table

[Cui Yuzhu]

Dear Eric,

Thank you very much for your explanation.

Changing the order of DPFU and Poly means: for example, I create two GC tables, GC1 and GC2.
in GC1, DPFU=0.01,Poly=1;
In GC2, DPFU=1, Poly =0.01.
I expect these two GC table will bring same result. But in reality, they are different.

To test this, in page 2, I created 19 GC tables in this way.
After calibration in AIPS, I output the data and load them to DIFMAP to check the gain factor by GSCALE.
The offset is the gain factor obtained for each data with different GC table.

For GC 1 to GC 10, they are all with fixed poly =1. I changed DPFU. The amplitude is inverse 
proportion to DPFU (G in the formulae in page 2). That is consistent with the expectation.

For GC 11 to GC 19, they are all with fixed DPFU=1. I changed Poly. But the results are same.
So I guess when we have only one parameter in Poly which represent the DPFU is constant with the elevation,
AIPS will scale the poly to 1 no matter what value it originally is.

Is this right?

Best regards,
Yuzhu





> 在 2019年6月22日，00:09，Eric Greisen <egreisen at nrao.edu> 写道：
> 
> On 06/21/2019 02:44 AM, Cui Yuzhu wrote:
>> Dear Eric,
>> Yes, as I change the NCOUNT, more parameters are shown.
>> For the relation between DPFU and Poly, I will wait for your further comments.
> 
> The polynomial is an expression that computes a relative value as a function of elevation (or other possible "Y" parameters).  This is then scaled by a scalar number - the sensitivity in K/Jy.  The GC table contains in the gain curve column Nterms of the polynomial for each IF in a polarization and there is a second column for a second polarization (if present). Our subroutine TABGC combines the 2 polarizations into single variables.
> 
> I don't understand what you mean by change the order of these two parameters.  Surely Poly(elev) * DPFU is the same as DPFU * Poly(elev). I also do not understand "offset" in pages 2 and 3.  Perhaps the issue is not seeing all that is contained in the GC table.
> 
> Read $YPGNOT/APCAL.FOR subroutine GCVAL to see how the values in the GC table are used to compute a predicted gain for each antenna.
> 
> Eric Greisen

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