Guide to Running Configure
There are a number of options available within the Configure algorithm. These are illustrated in Figure 1.
Annealing. This governs how quickly the annealing routine cools during the allocation process. The Standard setting is generally fine.
Weight close pairs: ThetaMin; ThetaMax. In some circumstances one may wish to give additional weight to closely packed targets, at the expense of overall target yield. These allow this to be setup, but beware of the odd effects it will have on your allocation. This option has not been extensively tested to date.
Cross beam switching. If the observation requires Cross Beam Switching (CBS) between pairs of fibres, then the user should first generate the paired target positions using the menu option Commands->Generate CBS pairs and then set the CrossBeamSwitching flag. This gives additional weight to targets which are successfully allocated pairs of fibres, at the expense of overall target yield.
Straighten fibres. This gives increased weight to allocations which have fewer fibre crossovers. While this will have some impact of target yield, the effect is small/undetectable for most source distributions and results in fields that typically require fewer fibre parks between configurations, hence reconfiguration is faster (perhaps by 10minutes, ~20%, in some cases). Fig. 13 of Miszalski, Shortridge and Saunders et al. (MNRAS, 2006, 371, 1537), (arXiv:astro-ph/0607125) shows the effects of this straightening. It can have adverse effects on target priorities and so the concerned user will need to experiment with this option to determine the optimal solution.
Collision Matrix. It is occasionally useful to save the matrix of fibre collisions which has been calculated for this field. This enables quick restarts of the software later on. This file can however be rather large.
Enforce sky quota. This option forces the allocation of the requested number of sky fibres. This can result in subtly lower target yields for some fields, although the effect is small/undetectable for most source distributions (accepting that the full sky quota is allocated to skies). Most datasets will be of little value with less than 15 sky fibres. 20-30 fibres is more typical for most projects.
Peripheral weighting for Fiducials. This gives enhanced weight to selection of stars towards the edge of the field, which is typically beneficial for acquisition, and prevents all of the fiducial stars being crowded into a small area of the plate, as can happen with the SAconfigure algorithm.
Weight fiducial target pairs. For CBS observations one may wish to allocate the fiducial fibres in pairs in order to guide in both positions of the beam switch. Setting this flag gives extra weight to paired fiducial allocation. Note: it is often more efficient in terms of fibre allocation for the user to allocate fiducials by hand but to ensure that half of the fibres (e.g. 50, 150, 250 and 350) go to position A guide stars, while the other half (e.g. 100, 200, 300 and 400) go to position B guide stars. There is no requirement that these stars be the same set in the A and B positions.
Number of background threads to use. The calculation of the fibre collision matrix is very CPU intensive. On a modern multi CPU machine Configure can hijack all of the available CPUs and run a number of background threads, this vastly reduces the allocation time. For a single CPU machine, there is nothing to gain here.
On-the-fly collision calculation. By default, the the collision matrix is calculated in full in advance of the annealing (this is the way Configure-v7.4 operated when SAconfigure was first introduced). An alternative is to calculate it on-the-fly. This ensures that A configuration is achieved as quickly as possible. This configuration will be HIGHLY sub-optimal. The longer the process is allowed to run, the greater the region of parameter space that is investigate and the the better configuration will be. In the limit of the annealing process, the two approaches will produce identically good configurations, and will take identically long to reach this point. There is therefore often little point in doing the calculations on-the-fly. In fact this option may allow inexperienced/inpatient users to produce sub-optimal configurations. It can however, be used in cases where a pretty good configuration is needed rapidly. Note: the original Oxford configuration algorithm, which can be used instead of the annealing by running the configureTrad command, will be far quicker.
Number of Sky fibres. The indicated number of sky fibres will be assigned (but see the note above on enforcing the sky fibre quota).
Figure 1: Allocation options in Configure
Additional Expert allocation options
These options can only be accessed via the Expert user mode which one activates via the toggle setting in the Options menu. These settings are generally for support astronomers and expert users. These are illustrated in Figure 2.
Fibre clearance, Button clearance and pivot angle. These options are mainly for the 2dF support staff. If you do not know what they are used for then you should not adjust them. Note that the 2dF robot has safe values HARD WIRED into the system and so a configuration which is outside these bounds will be flagged as INVALID at configuration time. These settings should only be used to restrict the values to tighter constraints for reasons that are beyond the scope of this web page.
Random Seed and Percentage of allocations sampled. If one needs to configure more quickly, e.g. if the field is pathologically complex (usually centrally condensed or with heavily clustered targets) and one cannot alter fibre allocations as described above (and on the complex configurations page), then it is possible to sparse sample the collision matrix and speed up the process. The details of this option are beyond the scope of this web page and should be discussed with your support astronomer. The principle is, for such configurations, that the slow speed is caused by the large number of rather similar configuration that are available (in essence many objects could be configured with many different fibres without changing the basic properties of the configuration). The sparse sampling reduces the number of available allocations for these heavily oversampled objects, but does not remove the object from the possible allocations. Note that at this time the effect of this sparse sampling on properties such as spatial clustering is unknown. In most cases a better construction of the .fld file, with serious thought given the the true requirements of the project, is more appropriate than using sparse sampling on a poorly defined input file. To use the sparse sampling, set the seed for the random number generator, and then set the percentage of allocations to sample. Using only 10% will result in a very quick configuration, but most likely a poor yield. Using 80% seems to give a significant improvement in speed, without an obvious detrimental effects on the yield. Note: this mode is still underdevelopment, and it's effects are poorly understood at this time.
Figure 2: Expert Allocation options in Configure
Sarah Brough (firstname.lastname@example.org)