[daip] AIPS limitations for large numbers of antennas

[Eric Greisen]

Lynn Matthews wrote:
> I'm gearing up to do some experiments using simulated u-v data sets, some 
> of which might include up to a few hundred stations. In anticipation 
> of this, I've been trying to better understand what the limitations of 
> AIPS would be for imaging and otherwise manipulating these kinds of data.
> In short, is there hope that this could work?
> 
> In some experiments I've done so far, I find that, e.g., IMAGR seems happy 
> imaging a u-v data set with 500 stations---until the end when it prints a 
> series of messages of the type:
> 
> IMAGR2 15:26:35 GETANT: STATION NUMBER    91 FOR ENTRY=  91 SUBA=  1
> 
> for all stations with ant # >90. What are the actual repercussions of 
> this? Is this N=90 limit one that could be modified?
> 
> Obviously the arrays ANTENNAS and BASELINE allow a maximum of 50 elements, 
> but in some other tests I seem to be encountering some problems even 
> staying within those limits. For example, if I take a large-N u-v data set 
> and attempt to extract a subset of the antennas using UVCOP, I find that 
> if I try to extract, say 35 antennas & baselines, not all of the 
> visibilities are copied. For N~40, there is a series of messages of the 
> type:
> 
> UVCOP2: ZCLOSE: LUN = 39 ALREADY CLOSED IN FTAB ON SEARCH
> 
> and for N=50:
> 
> ZMSGCL: LUN =  6 ALREADY CLOSED IN FTAB ON SEARCH
> ZTTYIO: LUN =            6  NOT OPEN IN FTAB
> 
> after which the program hangs for a while and loses an even larger 
> fraction of the visibilities. Is this due to some additional constraint on 
> the total number of baselines allowed?

Ther is a fundamental limit of ~250 antennas due to the method by which 
the "baseline" is recorded (256 * IA1 + IA2).  There is a correctable 
limit of 90 antennas which is compiled into the code from a PARAMETER 
statement on MAXANT in PUVD.INC.  I know of no reason for UVCOP to have 
the problems you report.  I cannot find an LUN 39 in the task (doesn't 
mean it is not there but hard to find) and the 2nd message suggests that
the message area has been overwritten.

Eric Greisen