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Example 2.16: Using Supplementary Resources

In this example, the same project as in Example 2.15 is scheduled with a specification of DELAY=0. This indicates to PROC CPM that a supplementary level of resources is to be used if an activity cannot be scheduled to start on or before its latest start time (as computed in the unconstrained case). The schedule data and resource usage data are saved in the data sets WIDGO16 and WIDGRO16, respectively. They are displayed in Output 2.16.1 and Output 2.16.2, respectively.

   title 'Using Supplementary Resources';
   proc cpm date='02dec91'd interval=weekday
            data=widgres holidata=holdata resin=widgrin
            out=widgo16 resout=widgro16;
      tailnode tail;
      duration days;
      headnode head;
      holiday hol;
      resource engineer engcost / period=per obstype=otype
                                  cumusage
                                  delay=0
                                  delayanalysis
                                  routnobreak;
      id task;
      run;

To analyze the results of the resource constrained scheduling, you must examine both output data sets, WIDGRO16 and WIDGO16. The negative values for Aengineer in observation numbers 22 through 25 of the Usage data set WIDGRO16 indicate the amount of supplementary resource that is needed on December 23, 24, 25, and 26, to allow the project to be completed without delaying any activity beyond its latest start time. Examination of the SUPPL_R variable in the Schedule data set WIDGO16 indicates that the activity, `Prototype', is scheduled to start on December 23 by using a supplementary level of the resource engineer.

Note that the supplementary level is used only if the activity would otherwise get delayed beyond L_START + DELAY. Thus, the activity `Anal. Market' is delayed by five days (S_START = `16DEC91') and scheduled later than its early start time (E_START = `09DEC91'), even though a supplementary level of the resource could have been used to start the activity earlier, because the activity's L_START time is equal to `22JAN92' and DELAY = 0.

Further, note the use of the option CUMUSAGE in the RESOURCE statement, requesting that cumulative resource usage be saved in the Usage data set for consumable resources. Thus, for the consumable resource engcost, the procedure saves the cumulative resource usage in the variables Eengcost, Lengcost, and Rengcost, respectively. For instance, Eengcost in a given observation specifies the cumulative value of engcost for the early start schedule through the end of the previous day.

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