<div dir="ltr">I'm guessing that the problem is, as Cormac suggested, that there are LWA-LWA baselines that have a 9.8 MHz bandwidth, and difx2fits can't build a valid FITS file with both those and 8 MHz bands. printDiFXInput is a good summary tool, which is easier than diving into the baseline table directly and working backwards to figure out if you have any offending baselines being correlated.<div><br></div><div>Cheers,</div><div>Adam</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, 24 Mar 2021 at 22:43, Jan Wagner via Difx-users <<a href="mailto:difx-users@listmgr.nrao.edu">difx-users@listmgr.nrao.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi Jayce,<br>
<br>
you could use "printDiFXInput.py <inputfile>" from either DiFX 2.6.2<br>
or for more details DiFX Trunk. That will show you the list of<br>
datastreams and their recorded plus zoom frequencies, and a summary<br>
of the baseline table showing the frequencies that are expected to<br>
be found in the *.difx/DIFX_... output files.<br>
<br>
Similarly, "printDiFX.py <difxfile>" lists the visibility records in<br>
the mpifxcorr output files. Maybe some frequencies there are<br>
"unexpected"?<br>
<br>
Depending on how difx2fits was compiled and whether you have the gdb<br>
debugger installed, you could "gdb --args difx2fits -d test.fits"<br>
and type "run" in the gdb console. After the crash, type "bt" in the<br>
same gdb console. That might produce a more detailed explanation<br>
(for developers) of what could have provoked the segfault.<br>
<br>
regards,<br>
Jan<br>
<br>
Am 24.03.2021 um 02:10 schrieb Jayce Dowell via Difx-users:<br>
> Hi Adam & Chris,<br>
><br>
> I've moved on to the VLA+LWA data and am running into a new<br>
> problem. I have my frequency setups as:<br>
><br>
> # FREQ TABLE #######!<br>
> FREQ ENTRIES: 2<br>
> FREQ (MHZ) 0: 71.09999999441<br>
> BW (MHZ) 0: 9.80000000000<br>
> SIDEBAND 0: U<br>
> NUM CHANNELS 0: 392<br>
> CHANS TO AVG 0: 1<br>
> OVERSAMPLE FAC. 0: 1<br>
> DECIMATION FAC. 0: 1<br>
> PHASE CALS 0 OUT: 0<br>
> FREQ (MHZ) 1: 71.99999999441<br>
> BW (MHZ) 1: 8.00000000000<br>
> SIDEBAND 1: U<br>
> NUM CHANNELS 1: 320<br>
> CHANS TO AVG 1: 1<br>
> OVERSAMPLE FAC. 1: 1<br>
> DECIMATION FAC. 1: 1<br>
> PHASE CALS 1 OUT: 0<br>
><br>
> In my data streams table I have the LWA stations recording complex<br>
> double sideband with frequency setup 0 and one zoom band of setup<br>
> 1. The VLA antennas are set real upper sideband with frequency<br>
> setup 1 and no zoom band. I think this is what I want and<br>
> mpifxcorr doesn't complain when I run it. However, difx2fits<br>
> immediately segfaults when I try to build a FITS-IDI file. Any<br>
> suggestions?<br>
><br>
> Jayce<br>
> -- <br>
> On 3/10/21 4:19 PM, Adam Deller wrote:<br>
>> * [EXTERNAL]*<br>
>><br>
>> **<br>
>> Glad to hear it!<br>
>><br>
>> On Thu, 11 Mar 2021 at 09:58, Jayce Dowell <<a href="mailto:jdowell@unm.edu" target="_blank">jdowell@unm.edu</a><br>
>> <mailto:<a href="mailto:jdowell@unm.edu" target="_blank">jdowell@unm.edu</a>>> wrote:<br>
>><br>
>> Hi Chris,<br>
>><br>
>> After some digging I was able to get to the bottom of this<br>
>> and I am now<br>
>> getting results that I am happy with. It was a combination of<br>
>> switching<br>
>> over to trunk and fixing a bad assumption in my VDIF<br>
>> conversion that<br>
>> everyone represents four-bit complex integers in the same way.<br>
>><br>
>> Jayce<br>
>> --<br>
>> On 2/4/21 3:08 PM, Phillips, Chris (CASS, Marsfield) wrote:<br>
>> > [EXTERNAL]<br>
>> ><br>
>> > Hi Jayce<br>
>> ><br>
>> > I'm working the data from the Long Wavelength Array and I am<br>
>> trying to see if we can move from our homegrown correlator to<br>
>> DiFX. The two modes I need to support are a LWA-only mode<br>
>> with homogeneous<br>
>> data and an "eLWA" mode with heterogeneous data that combines<br>
>> the<br>
>> LWA stations with the VLA 4-band system. For the LWA-only<br>
>> mode I<br>
>> have 4+4-bit complex voltage data from two 19.6 MHz wide<br>
>> spectral<br>
>> windows. I am currently converting these data from the LWA<br>
>> format<br>
>> into two VDIF files, one per window, for correlation with<br>
>> DiFX. My<br>
>> .input file describes the data as:<br>
>> >><br>
>> >> DATA FORMAT: INTERLACEDVDIF/0:1<br>
>> >> QUANTISATION BITS: 4<br>
>> >> DATA FRAME SIZE: 7872<br>
>> >> DATA SAMPLING: COMPLEX_DSB<br>
>> >> DATA SOURCE: FILE<br>
>> >><br>
>> ><br>
>> > I have never personally tested complex_dsb data with<br>
>> interlaced<br>
>> vdif. I have no idea if there could be any “interaction” with<br>
>> the<br>
>> VDIF interleaving and the specific data type (I would have<br>
>> thought<br>
>> not, but you never know).<br>
>> ><br>
>> > The issue could also be with interpreting the interlaced<br>
>> VDIF,<br>
>> not the complex double sideband.<br>
>> ><br>
>> > Once you have tested using trunk, not the released version, I<br>
>> would try and use some of the vdifio utilities to try and<br>
>> convert<br>
>> the interlaced VDIF into plain VDIF - either extracting out one<br>
>> thread, or merging into multichannel single thread VDIF. You<br>
>> would<br>
>> obviously need to update the DIFX .input (and or .v2d) file and<br>
>> vexfile to match the new setup.<br>
>> ><br>
>> > I would also be using the m5access tools to do things like<br>
>> make<br>
>> the autocorrelation (both before and after fiddling with the<br>
>> data<br>
>> layout). Check DIFX gives the same auto shape as you get with<br>
>> m5spec. If you use a modulated noise source, folding the data<br>
>> (m5fold) on the period of the noise cal can be very informative<br>
>> also. Also look at the headers and check that the #<br>
>> frames/sec etc<br>
>> are what you expect (before and after merging threads etc).<br>
>> If you<br>
>> decide it is the interlacing is the issue, I suspect you will<br>
>> need<br>
>> to discuss with Walter.<br>
>> ><br>
>> ><br>
>> >> I am less sure about DiFX supporting our eLWA mode. For<br>
>> this we<br>
>> have the same 4+4-bit complex voltage data from the LWA<br>
>> stations but<br>
>> with a bandwidth of 9.8 MHz. We are combining this with<br>
>> 4-bit real<br>
>> voltages from the VLA with 8 MHz of bandwidth and a slightly<br>
>> different frequency setup. We currently process these data by<br>
>> shifting the center frequency of the LWA data to match that<br>
>> of the<br>
>> VLA, running two F-engines with different channelization to<br>
>> arrive<br>
>> at the same channel width for both data sources, and then cross<br>
>> correlate what overlaps. Is this mode something that DiFX<br>
>> supports?<br>
>> >><br>
>> ><br>
>> > Can you represent this data as VDIF? If you you can probably<br>
>> handle the different setup using zoom bands. However if this<br>
>> can be<br>
>> done will really depend on the EXACT setup. Basically you<br>
>> need to be<br>
>> able to channelise the two setups with the same final frequency<br>
>> resolution (ie different FFT sizes will be needed, with the<br>
>> ratio of<br>
>> the FFT size matching the ratio of the bandwidth difference.<br>
>> But the<br>
>> sky frequency of the frequency points out of the FFT need to<br>
>> match<br>
>> exactly (ie even if you could achieve the same frequency<br>
>> resolution,<br>
>> if the fine channels are offset by 1/3 of a channel you will<br>
>> have<br>
>> problems (if that offset is a simple integer ratio, you can<br>
>> just use<br>
>> a higher frequency resolution)<br>
>> ><br>
>> > I hope this makes sense.<br>
>> ><br>
>> > Cheers<br>
>> > Chris<br>
>> ><br>
>><br>
>><br>
>><br>
>> -- <br>
>> !=============================================================!<br>
>> A/Prof. Adam Deller<br>
>> ARC Future Fellow<br>
>> Centre for Astrophysics & Supercomputing<br>
>> Swinburne University of Technology<br>
>> John St, Hawthorn VIC 3122 Australia<br>
>> phone: +61 3 9214 5307<br>
>> fax: +61 3 9214 8797<br>
>><br>
>> office days (usually): Mon-Thu<br>
>> !=============================================================!<br>
><br>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px">!=============================================================!<br><div dir="ltr" style="font-size:12.8px">A/Prof. Adam Deller </div><div dir="ltr" style="font-size:12.8px">ARC Future Fellow</div></div><div style="font-size:12.8px">Centre for Astrophysics & Supercomputing </div><div dir="ltr" style="font-size:12.8px">Swinburne University of Technology <br>John St, Hawthorn VIC 3122 Australia</div><div style="font-size:12.8px">phone: +61 3 9214 5307</div><div style="font-size:12.8px">fax: +61 3 9214 8797</div><div style="font-size:12.8px"><br></div><div style="font-size:12.8px">office days (usually): Mon-Thu<br>!=============================================================!</div></div></div></div></div></div></div></div></div></div></div></div></div></div></div>