Run Control: new outer loop do optimization, scanning etc.

Discussion about coding and new developments
Post Reply
raback
Site Admin
Posts: 3670
Joined: 22 Aug 2009, 11:57
Antispam: Yes
Location: Espoo, Finland
Contact:

Run Control: new outer loop do optimization, scanning etc.

Post by raback » 26 May 2020, 01:05

Hi All,

There are some new developments related to optimization, parameter scanning and beyond, of multiple Elmer simulations in "devel" branch. This involves new section ”Run Control”. This is a special section in the way that it is analyzed before the rest of the simulation is carried out.

For example, test case "ParamFourHeaters" has the following section that will run the case four times altering the parameters as defined in ascii table par.dat

Code: Select all

Run Control
  Run Control Iterations = Integer 4
  ! give parameters as an ascii matrix:
  Parameter File = File "par.dat"
  Parameter Count = Integer 4 ! columns in matrix
  Parameter Row Offset = Integer 2 ! starts from line 3
End
The parameters are then available as "rpar" vector for following matc expressions (starting with $ or MATC). For example, the first parameter sets the heat source 1 in the test case:

Code: Select all

Body Force 1
  Name = "Heater1"
  Heat Source = $rpar(0)
End
By construction the "Run Control" section is read first, and then the MATC vector is created. The sif file is reanalyzed meaning that all dependent variables may also change. The good thing with this approach is that constants may be truly constants i.e. time is not spent in analyzing variables. A minor limitation is that "Run Control" section must preceed all other sections.

The parameters may also be generated by internal optimization procedures. The routines in the old FindOptimum solver has been copy-pasted & slightly modified to provide simple internal optimization routines. For example, in test case "OptimizeSimplexFourHeatersInt" we have:

Code: Select all

Run Control
  Run Control Iterations = Integer 100
  Parameter Count = Integer 4
  Parameter Optimal Finish = Logical True
  Parameter Best File = File "optimize-best.dat"
  Parameter History File = File "optimize-history.dat"
  Cost Function = Variable Time
    Real Procedure "CostFunction" "CostFunction"
  Optimization Method = String "simplex"
  Simplex Relative Length Scale = Real 1.0
End
Again the parameter $rpar() is used in the following sections and simplex method is used for 100 simulations. The history and best configuration are saved.

Traditionally Elmer has had time dependency mode "scanning" that has enabled simple sweeps over parameters. This can now be achieved also with the new "Run Control". Test case "HelmholtzPlaneWavesParam" demonstrates how to scan over frequency space. The key line is

Code: Select all

  Frequency = Variable "run"
    Real MATC "1000*tx"
i.e. the loop parameter is available as variable "run" for all dependency models.

So why did the old "scanning" mode not do the work? It perhaps could have done it for steady state cases. The problem is that it used the time as a pseudo variable which meant that it was impossible to study transient systems. This can deal with transient cases (the initialization may need to be checked).

So why now do everything externally? That might be the ideal modular way to work. However, there may be additional features that you can do when everything is internal also concerning the history. Also some redundant pre and post tasks are eliminated. There is no strong case for this but with this rather modest work, why not have an internal option?

An example of something more non-conventional use of "Run Control" is found in test case "RunControlStructured". There
a simple 3D heat equation is solved and the boundary conditions between different runs are inherited from
the other end of the cube.

We are open for comments & ideas. Do you have any idea how this additional outer control level could be used?

-Peter

Post Reply