How SSA Calculations are Done

Suppose that the whole dynamic simulation must be solved N times because there are N different sets of parameter values. Each scenario is solved in a subdirectory SSASIMDIRx (x=1,2,3 etc) of the Temporary Directory.

First RunDynam produces files containing the N different sets of varying parameters. For example, if parameters on logical file GTAPPARM are varying, RunDynam will produce N different versions of the original GTAPPARM file. Each solve (dynamic sim) is the same as the original one except that one of these N versions of the GTAPPARM file is used in place of the original one.

RunDynam can carry out several SSA solves concurrently and this will reduce the time taken if you have a computer with several processors. Each solve fully occupies a single processor. The solve is done in order of periods, starting from the first, moving towards the last one. Each period is solved in the order Base, Rerun (if done), Policy.

The progress report on the bottom panel of RunDynam shows which SSA runs are currently being done and how far each has progressed. For example you may see something like:

Param/Stroud SSA runs: 3(Period24), 4(Period 6)

[Need total of 8 SSA runs. Each run has 40 periods.]

This means that RunDynam is currently doing runs number 3 and 4 out of 8 runs needed. [The first and second runs must have finished.] The 3rd run is doing period number 24 (it may be doing the Base, Rerun or Policy - this report does not tell you which) while the 4th run is doing period number 6 out of 40 periods.

Suppose, for example, that you have 6 effective processors on your computer and that your computer is otherwise unused. When you carried out the original dynamic simulation, you probably told RunDynam to allow 3 concurrent solves (see the Run Preferences menu). That more-or-less reduced the time for the original simulation by one-third. When doing SSA, you can allow RunDynam to use all 6 processors (you indicate that on the same form as you use to choose the quadrature). Solving the model 20 times (for SSA) would take about 20 times as long as the original simulation if only one processor was used, so solving it 20 times for SSA will take about 10 times as long as the original solve took using 3 processors.

Working out the N different parameter files is done via a single run of the program SAVPFA.EXE (which must be in the directory in which RunDynam is installed).

Calculating the means and standard deviation results is done by RunDynam itself. [A Fortran EXE is not used.]

Program REPSOL2A.EXE is used to put the SSA means and standard deviation results into the Solution files which contain the SSA results.

Programs Required for SSA

The programs SAVPFA.EXE and REPSOL2A.EXE must be in the directory in which RunDynam is installed.

SAVPFA.EXE is needed for working out the varying parameter files.

REPSOL2A.EXE is used to put the SSA means and standard deviation results into the Solution files which contain the SSA results.

URL of this topic: www.copsmodels.com/webhelp/rundynam/hc_rundssacalcdetails.htm

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