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 LP Procedure

Use

The LP procedure is an optimization procedure used in the medium to long-term planning horizon for multiline planning(planning line networks with groups of alternative lines) to create period packages.

However, you can also use the LP procedure to plan linear line networks. This makes sense if you want to ensure that not only the restrictions that you have defined for the planning segment but also those that you have defined for the remaining lines of the line network are taken into account. See also: Single-Line Planning .

The complete mathematical description of this procedure is mixed whole-number linear program .

The LP procedure distributes the orders over lines and days. It creates an optimal assignment of planned orders (with lot sizes greater or equal to 1), cumulated per day or shift, to the possible processing paths of the products of a line network taking restrictions and capacities into account.

Caution Caution

When using the LP procedure, you cannot freely choose the planning segment in the line network. In this case, the planning segment always has to be the first segment of the line network irrespective of whether you are dealing with a line or a group of alternative lines

End of the caution.

Integration

You can execute this procedure by including it in a procedure package for the model mix planning run in Customizing for Model Mix Planning . You should choose the setting Requirements-oriented per shift or day as the planning basis of the horizon in the procedure package.

The procedure is defined in function module /SAPAPO/SEQH_LP01_CALL and uses the table /SAPAPO/SEQC_LPV.

Parameters

For the optimization, you can save various parameters in procedure profile for the LP procedure in Customizing for Model Mix Planning. The following parameters must be taken into account by the optimization:

  • Line capacity

    As a basic rule, the capacity of a line resource is taken into account by the LP procedure as a hard priority.

  • Restrictions

    The procedure takes into account the minimum and maximum values you defined in restriction maintenance as quantity restrictions .

    Additionally, the procedure can take the following restriction categories into account:

    • Spacing restriction

    • K-in-M restriction

    • Position restriction

      These restriction categories are converted internally into quantity restrictions . However, you must define this conversion in restriction maintenance.

      The number of hard restrictions should be kept to a minimum because the system would otherwise find it difficult to find a solution in the case of complex line networks and different production versions.

      The LP procedure takes the Hard indicator (which you set for restrictions) into account for maximum specifications only. Minimum values are taken into account as soft with priority 1. If, for example, you have specified in a restriction that at least 5 and a maximum of 15 vehicles with air conditioning can be built in a shift and you set this as a hard restriction, the LP procedure only considers the maximum value as a hard restriction that must not be violated.

      See also: Including Restrictions in Planning

  • Violations

    Violations of the capacities, restrictions, or desired dates/times are generally not rectified in the horizon. Instead, the system moves the affected orders to the end of the horizon that you have specified for the procedure. If an order cannot be scheduled in a certain bucket (day or shift) due to the violation of a restriction, the order is loaded at the end of the horizon. This may lead to undercoverage situations (shortages) in the horizon. To avoid hard date/time violations, with the already mentioned undercoverages, you must specify the number of days that you have specified for the horizon of the procedure for the parameters Max. Lateness and Max. Earliness in the Procedure Profile of the LP Procedure in the Weighting of Desired Date/Time in each case. If you have specified that the horizon should cover 10 days, for example, enter 10 days each for Max. Earliness and Max. Lateness .

Features

The goals of optimization with the LP procedure are:

  • Compliance with all restrictions that are defined as hard.

  • Minimization of the penalty costs that you have assigned to the restrictions that are defined as soft. You can specify the penalty costs by weighting the restrictions accordingly. Soft with the priority 9 leads to the lowest penalty costs and hard with priority the priority 0 involves to the highest penalty costs.

  • Minimization of earliness or lateness with regard to the customer’s desired date/time. That is to say, the planned orders should be scheduled in such a way that the availability date/time of the finished product is as close as possible to the customer’s desired date/time.

  • Minimization of the costs with regard to line priorities. This means that if you have specified priorities when maintaining the partial line network for alternative lines, planning attempts to schedule orders giving preference to the line with priority 1.

  • A smoothing procedure is integrated in the LP procedure. For this smoothing procedure, you can specify whether the system is to mix the products evenly when scheduling the orders or whether it should endeavor to adhere to customers' desired dates/times. See also: Defining Priority for Smoothing Procedure

  • If the number of orders to be scheduled per day/shift is less than the minimum quantity stipulated per day/shift, the system can respond as follows, depending on how the restriction is weighted:

    • If the restriction is a hard one (weighting 0), the optimization process terminates.

    • If you have not set a hard weighting, a shortfall below the minimum quantities only leads to penalty points.

    • If the minimum quantity that you defined per day or shift exceeds the line capacity, the system automatically uses the largest quantity possible as the minimum quantity. If the maximum quantity you defined per day or shift exceeds the line capacity, the system also uses the maximum possible quantity in terms of capacity.

    • Because the LP procedure attempts to distribute the products evenly on the line; it may happen that the system violates the minimum quantity stipulated in the quantity restriction.

  • Using the LP procedure, you can carry out model mix planning in the medium to long-term horizon as multiline planning . This means you can now also plan products which are produced together on a line network with alternative lines. Here, all lines and products that share the line network are viewed together and are scheduled taking restrictions and available capacity on the lines in the form of period packages (shift or period packages) into account.

    Note Note

    In an environment of large, complex line networks, performance may be impacted negatively. That is to say, in the extreme case, the optimization runtime may amount to several hours.

    End of the note.

  • Based on this planning result, the system can continue planning in the short-term horizon with the genetic algorithm or the prioritized equal distribution . In the process, the period packages are deleted and planned orders with lot size 1 created with exact start and end dates.

Activities

Multiline Planning with the LP Procedure