Scheduler Settings: Parameters

To access this dialog:

In the Scheduler Settings dialog, select the Parameters tab.

The parameters determine how the Scheduler conducts its search; the optimum parameters depend on the scheduling problem at hand. The default values often work best and you may want to try them before using other values.

About Activities

An Activity is a collection of contiguous blocks generated using the Pushback OES:

The size of an Activity is user defined in terms of mass and temporal extent
An Activity can include part of a bench or several benches.
The blocks are included in Activities in order defined by Pushback OES.

Field Details:

Basic schedule item (activity): the following three parameters control activity maximum size using different criteria. The actual physical activity size is set by Studio NPVS as a function of the complexity problem:

Maximum rock mass in an activity: choose a value between 1 and 10; larger values give smaller activities. The maximum rock mass in an activity is equivalent to the total available rock in a mine divided by the (supplied value * 50). For example, if the selected pit has a total rock mass of 50 million tonnes, setting a value of 2 will result in activities with a maximum mass of 500,000 tonnes.
Maximum time to complete activity: choose value between 1 and 10; larger values give smaller activities. Mine life is defined by the tonnage and the settings in the Time tab. The value that is used in activities will be the lower value of the following:
- 1/4 of the time period
- The mine life divided by (supplied value * 50)

For example, if Time is defined by 5Mt Total Rock per year (365 days), the mine life will be 10 years. Therefore, a value of 2 in the Maximum time to complete activity field calculates a value of 36.5 days. Why? because 92 days represents a quarter of a year and (10 years * 365 days per year)/(2*50) = 36.5 days, which is lower.

Maximum number of benches in one activity: when scheduling many pushbacks, it is usually preferable to set this parameter to larger values, say 4 or more. This sets the maximum number of benches in one activity. The value must be in the range 1 - 10.

Search properties: the following two parameters control the size and shape of the search tree:

Search extent: choose a value between 1 and 20; larger values allow for larger search trees but the searches will last longer.
Search breadth: Choose a value between 1 and 4. The optimum value depends on the problem; 2 works best for most problems. This value sets the number of arcs from each node in the scheduling 'tree'. A value of 2 makes a search tree with 2 branches from each node.
Rate Control Level: this is a technical parameter that determines how rate targets are checked in the first year of the schedule (it has no effect on ratio targets). The normal (High) option requires that the rate limits are satisfied after adding each new activity to the schedule starting at time 0. The Medium option starts enforcing the limits after 1/2 of the year; the Low options starts enforcing the bounds after 1 year. The last two options are generally used for Multimine projects to produce schedules when the first option does not find a solution.
Memory Control: In some cases, building a large tree may result in an "out of memory" situation. The Scheduler builds two search trees, each in two stages. First, a minimum tree containing at least one acceptable schedule is built and second, the tree is expanded to look for better schedules in terms of optimization objective (e.g. maximum NPV). This second tree may require too much memory; therefore, the "Save" option skips the expansion stage in this situation. As a result a schedule is generated although it is unlikely to be as practical as if normal expansion were carried out (using the Normal option).

In short, the Save option should be used when optimization in Normal mode has produced "out of memory" message during the expansion stage (where the output window displays the "expanding" message).

Re-schedule or set time limit

Restart: select to use a Pushback OES as input (do not re-schedule).

Reschedule from period: select to use a Scheduler OES as input and enter the year at which re-scheduling should start (can be 1).

Set schedule time limit: select this option to generate a new OES that considers only the blocks mined in the first X periods, where X is user defined

Reschedule from period and Set schedule time limit become available after the Scheduler OES is computed. Use Set schedule time limit in a new scenario as this cannot be reverted once the OES is computed within the time limit. This option is designed to be used for refining or validating a schedule with shorter time periods (quarters) based on a Life Of Mine schedule per year.

	Related Topics
	Capital Costs Scheduler Essentials Scheduler Quick Start

JMN 20065_01_EN