Linking SBs

Once the scheduling blocks (SBs) are created, you may have some conditional constraints for the execution of their observation(s). Linking SBs is done at the program block (PB) level (Figure 4.30). Under that PB there should be at least two SBs which are listed with an index number in the first column of the first table in the Scheduling Blocks section.

We call these SBs linked or conditional as they have some extra constraints. Up until now, this was accomplished by formulating these in the Comments to the Operator in each SB. For example, "Do not run this SB if SB# has already run" or "Run a combination of this SB and SB# for a total of x times (or y hours)". However, this communication is sensitive to errors and the preferred current method is to define Linked SBs.

Important Notes

• If an SB is removed (i.e., cut from the left-hand column list), the indexing of the SBs will be re-numbered. Therefore, all linked SBs should be double checked in case the re-numbering of the SB index affected those linked SBs. If those linked SBs received new indexes, then the constraint should be removed and a new constraint be added.
• If a linked SB is unsubmited, the conditional format will be automatically removed. Therefore, be sure to re-link the SBs.
  
• The SBs within a format statement are evaluated based on the LST start time, with a preference given to the SB in the list that has the earliest LST start time.

Common Examples

• For SBs targeting the same part of the sky but have different LST start ranges depending on the flux density calibrator that is included, run the SB that fits the LST start range (i.e., if it can't run within this LST start range, try running it in the other LST range). Conditional format example: Observe exactly one of the blocks (1,2)
• Run only one of the several SBs that are created for different weather conditions (i.e., don't run the SB with high-frequency resources when the weather is not suitable, but instead of waiting for the weather to improve, run a different SB with more relaxed weather constraints). Conditional format examples of this type are explained below under Figure 4.31.

How to Link SBs

To link SBs, enter the constraints in the Linked Scheduling Blocks interface above the table of SBs. Constraints are based on the index number of the SB and take the form of selecting those SBs and comparing it to a time or number of execution limit. Fly-over help is available for all of the fields. By adding constraints, a list of conditions is created that will run in priority from top to bottom (Figure 4.31). The priority order can be changed by selecting the constraint (highlights in blue) and dragging to the place it should be. Constraints can be removed by clicking on the Remove part of the constraint.

Once all constraints and priority order are satisfactory, the conditions have to be communicated to the system by clicking Stop Editing Constraints. This will notify the on-line system that conditions have been specified and will change the Stop Editing Constraints button into an Edit Constraints button for additional future editing if necessary.

Examples from Figure 4.31 Explained

• First four constraints: Observe exactly one of the blocks (43,44 / 45,46 / 47,48 / 49,50)
• This constraint tells the system that if this project is up for observing, first it should see if any of the SBs with index 43, 45, 47, or 49 would fit the LST start range and add it to the observing queue, if none of them has been run; it should only run one of them.
• Second constraint: Accumulate blocks (47,48,49,50) to a maximum total of 01:00:00
• If the first constraint has not selected any SB to run, the second constraint tells the system to select the SB from the list of index 47,48,49, or 50 that fits the LST start range (starting from left to right in the index list) and run this constraint as long as the total time does not cross 1h00m.

Note, adding no conditions at all, i.e., no linked SBs, is a valid option. We do not require SBs to be linked in order to be considered for observation.