|
 Printer Friendly |
Understanding Outputs: How output formulations affect model run times
Applies to: Woodstock 3.2x
Date: 05/15/2005
In Woodstock, outputs are the means by which you implement and evaluate management scenarios. It is important to be aware that your output formulations can have a significant impact on the time required for Woodstock to process the model, be it building a matrix or generating reports and graphs. The purpose of this tech tip is to describe the two types of Woodstock outputs, and how your choice of output formulation can influence model run times.
Outputs are either basic—the source statement references development types, actions and yields—or summary—the source statement references previously defined outputs. It is common practice in Woodstock to declare basic outputs for individual or groups of development types, actions, or yields and then use a summary output to calculate grand totals by summing the previously-defined basic outputs. It is the formulation of summary outputs that is the focus of this tech tip.
Suppose that you have a forest consisting of 3 districts, and that you wish to optimize wood flows for the entire forest and report wood flows at the district level. You formulate the district wood flow outputs as follows:
*OUTPUT oD1wood Wood flow from district 1
*SOURCE ? District1 ? aHarvest yWood
*OUTPUT oD2wood Wood flow from district 2
*SOURCE ? District2 ? aHarvest yWood
*OUTPUT oD3wood Wood flow from district 3
*SOURCE ? District3 ? aHarvest yWood
You can formulate the forest wide wood flow output either using a summary output:
[1]
*OUTPUT oForestWood Wood flow from forest (all districts)
*SOURCE oD1wood + oD2wood + oD3wood
or using a basic output:
[2]
*OUTPUT oForestWood Wood flow from forest (all districts)
*SOURCE ? ? ? aHarvest yWood
The two forest wood flow outputs above are effectively identical, but the work required to process them is very different. In the case of the summary forest wood flow output [1], for a given development type, Woodstock must check each of the basic outputs referenced in the source statement and determine if the development type matches the mask; that is, Woodstock must check three basic outputs to calculate the summary output. In the case of the basic forest wood flow output [2], Woodstock only needs to perform one check.
Summary outputs begin to impact model run times as the number of the Landscape themes and the number of summary outputs increase, both of which increase the number of checks described above. If you are optimizing or constraining a summary output, and not the basic outputs contained within it, you may benefit from reformulating the summary output as a basic output. This can potentially reduce the number of checks required to calculate the output and thus reduce model run times.
The upshot? It isn’t a problem to declare a large number of basic outputs in a Woodstock model, just be careful how you summarize them. You may be able to use Landscape aggregate attributes to create groups of basic attributes, and use masking in output declarations to calculate group totals rather than sums of previously defined outputs.
|
|
Stora Enso Predicts a 2.5% Savings
“We asked, ‘If we had made the decision and optimized the problems, how much money would we have saved?’” The answer was approximately 2.5 percent.”
- Continue reading...
- View all case studies...
|
 |
|
|
|
